Setting Honeywell Aquastat L8124A, C

HI, I have a Central Boiler outdoor wood furnace connected to an oil boiler with a baseboard hot water system. There is a Honeywell Aquastat L 8124A, on the oil boiler. There is three dials on the Aquastat, a Diff dial set at 12, a Hi dial set at 160 and a Lo dial set at 125. I do not know if these settings are correct or the most efficient. I am looking to get the settings correct so that the oil boiler comes on less. I also have a heat exchange plate between the wood furnace and the oil furnace. I don't know if that is important information to the question. I typically set the wood furnace at 190 degrees because I have a big old house with two long baseboard zones plus a hot water zone. Thanks Harry.

 

Hi Harry,

The best way to get the burner to fire less is to improve the building envelope such that the home loses heat more slowly! Insulation and air infiltration sealing.

The HIGH limit on the aquastat is 'typically' set up for 180F. This is because it's the 'standard' design temperature that the baseboards in the home are set up for. If properly designed, on the coldest day ('design day'), worst case conditions, there should be enough baseboard in the home in order to be able to offset the heat loss, and the baseboard output is usually spec'd at 180F AVERAGE water temperature.

If you are able to heat your home in the most extreme conditions with 160F, then leave the setting there. If you find the home cooling off when it gets real cold out, you can increase it if needed. I would not go much below 160 with the HIGH setting... and never closer than 20F to the LOW setting.

The DIFF dial acts ONLY in conjunction with the LOW setting. The HIGH has a FIXED DIFF and no knob for adjusting.

The type of aquastat that you have is called a 'triple' aquastat and is used mainly on boilers that also supply domestic hot water to the home via the use of a 'tankless coil' inside the boiler.

Does your boiler also supply domestic hot water?

If so, your LOW setting of 125F is enough to provide the home with adequate hot water? (it usually is NOT, that's why I'm asking...)

Since you have a wood boiler tied in to the system, perhaps you are looking to disable the oil burner when you are heating with wood? Is that what you are driving at? There are ways to do this with proper control applications.

Let us know how your domestic hot water is produced and we can go from there...

 

Hi, thanks for the reply. The wood furnace also heats the domestic hot water. I have a super store hot water tank next to the oil boiler. What I am trying to achieve is using the oil boiler as little as possible. Could I disable the oil boiler, just turn it off, and just use the wood furnace? Would the circulators still work if I turned of the oil boiler? In Massachusetts, it can get pretty cold and I like the idea of having the oil boiler back up system. If I set the high dial at 180F would that cause the oil boiler to go on more often. I have heard that some people with wood furnaces shut off their oil boilers. I am not sure how to do this? You indicated in your reply that I might be able to do this with proper control applications? Thanks again, I have learned something already from your reply I hope I'm providing the correct info. Harry

 

Your 'super store' is an INDIRECT water heater and is plumbed as a separate zone off the oil boiler?

Did the oil boiler USED TO provide the domestic hot water via a tankless coil in the boiler?

I'm trying to determine why you even have a 'triple' aquastat at all... if the system was converted to the indirect water heater the aquastat should have been changed out for a cold start model.

What is the make/model of the oil boiler?

More specifically, what is the make/model of the BURNER and does this burner have a Honeywell 'primary control' which has 2 terminals labeled " F F " with two yellow wires on them, and two terminals marked " T T " with a wire jumper across them?

If the system is wired per code, no, this won't work. Turning off power to the boiler should turn off ALL controls related to the boiler, pumps and all.

If you didn't have the wood burner, the answer would be no... the oiler would only fire up as needed to heat the home when the thermostats called for heat.

What I think you are trying to achieve by turning the HIGH setting down is to prevent the oil burner from firing when the woody is providing heated water to the system, in hopes that the wood burner always keeps the water temperature above the HIGH setting of the aquastat, thus preventing the burner from firing but still allowing the pumps to run to provide the heat to the home.

How exactly is the woody connected to the system? Is there a 'heat exchanger'?

Can you provide some sort of piping diagram?

Only if I have a very clear idea of the 'big picture' can I suggest much more...

 

Darb,
Just a thought. If your object is just to use the pumps and not the burner you can do this.
Shut off the power, lift up the transformer and remove the cad cell eye. By doing this your burner will run for 45 sec. and then shut down on reset which means the burner is disabled but not the pumps. Everything else will work normally except the burner will not fire.

There are other ways to do this but this doesn't involve removing wires.

Bear in mind that if you do this you will have to put the the cad cell back and reset in order to use the burner again.
This will not let the burner come on automatically if the wood stove goes out.

This will only disable the burner sothe t-stats and pumps can be used independently.

Just an uncomplicated idea.

 

Even less complicated would be not even opening the burner up and if the burner has the Honeywell primary control, just remove the jumper between T T to disable the burner.

This still would require action to get the burner going again (replacing the wire jumper) but I think easier than pulling the CAD cell, no?

More complicated, but:

An 'ideal' set up with a wood burner in conjunction with a 'normal' boiler would be one which AUTOMATICALLY selects the fuel...

This is usually accomplished with an aquastat on the piping coming to and from the wood burner. This aquastat would be set to something around 140F and would sense when there is a fire in the woody by the temp of the water.

The aquastat can then be wired to the normal boiler in such a way as to enable/disable the burner when there is a fire in the woody.

 

Troop,
I didn't mention the cad cell wires because he's got the 8124 and your in there with line voltage.
As for the aquastat your exactly right but my post was long enough and figured if he showed any interest we could have per sued that option.

A little off point but I did set up a wood burner with a furnace that way. A friend had a wood stove next to the furnace we had just put in and taking a page from your book, we sat down to appreciate the fruits of our labor over a few ice cold drafts from his newly installed tap system we just put in.

In conversation he mentioned it would be nice to have the wood stove heat go upstairs.
A few beers later the light came on. Being a welder, he welded up and hung a steel enclosure over the wood stove.
We cut a hole and ran a pipe into the return trunk of the furnace. I installed a fan/limit switch into the enclosure and wired it into the blower circuit bypassing the the burner.
As long as the wood stove was on the blower was on. When the stove went down the f/l switch shut off and the burner came on.
Everything automatic, worked like a charm.

 

Hi NJ Trooper, I have a Peerless oil boiler and a Beckett burner with a Honeywell intermittent ignition on top of the burner. There are two yellow wires on the FF side and a black jumper wire on the TT side. The oil boiler and the Super Store were installed new 15-20 years ago by a licensed contractor. The Honeywell triple aquastat came with the oil boiler installation.

There is a metal plate to plate heat exchanger next to the oil boiler. The supply to the oil boiler goes to the top of the oil boiler and the return from the oil boiler is on the bottom. There is a circulator on the return pipe from the oil boiler pushing the return water to the heat exchanger. The woody hot water supply heats up the oil boiler supply water via heat exchanging between the metal plates. There are 4 temp gauges on the heat exchanger on the supply lines and the return lines to show the water temp after it goes through the heat exchanger. Thanks Harry

 

Hi NJ TRooper, removing the jumper wire would be an easier option for me than trying to remove the cad eye cell. I am not familiar with the cad eye cell and would not be comfortable with removing it. Thanks for all your help.

 

Hi, thanks for the info, I am not familiar with the cad eye cell and would not feel comfortable removing it. I would have to see one first. I will try the internet or a pumping supply place. Thanks again Harry.

 

Darb, is it possible to show us some pics of the install? It will help with the advice we give.

When the woody is running and the water is hot, I know that the pump from the woody is always running.

Is there also constant circulation between the oil side of the heat exchange and the boiler? In other words, does the oil boiler stay hot whenever the woody is burning? This would be ideal in my opinion as the boiler is a good place to 'store' some BTUs from the woody.

OR, is there no circulation through the heat exchanger on the boiler side until a thermostat calls for heat?

What kind of temperatures do you typically see on the thermometers?

I don't understand why... you've been burning more oil than you should have been for all these years. Your boiler should have been set up as a 'cold start' at time of installation, even if it meant swapping out the 8124 for an 8148.

There IS a way to convert the 8124 for cold start, are you interested in that?

If I were you and did not feel comfortable 'messing' with the internals of the burner, then don't do it.

 

Hi, what do you mean by setting the oil boiler up for a cold start? I would be interested in converting the 8124 if it is not to complicated. Thanks Harry.

I can take pics of the oil boiler and the woody. I'm not sure if I can send them correctly. If you could walk me through the Forum part of sending pics I would appreciate it. I checked the circulator at the bottom of the furnace that goes to the metal heat exchanger and it appears that it runs constantly. I'm assuming that the water in the oil furnace is constantly heated. The supply from the woody is usually 180 +, the supply side of the oil boiler is around 160 to 180 depending on if the circulators are running at the time. The return of the woody is around 160+/- and the return on the oil boiler is around 160 to180. Thanks

 

Hi NJ Trooper, I disconnected the black loop wire on the TT side of the ignition on top of the burner. It seems to be working fine, circulating the hot water through the two baseboard zones and the domestic hot water zone. The oil burner is not coming on and the house is generally warmer from the constant/consistent hot water flowing through the zones. I have the woody set at 190 and the oil boiler aquastat set at 170 H, 125 Lo and 10 Diff. I live in an old 10 room farm house. I have in the past done what I could to increase the insulation, storm windows, etc. Thanks for your good advice, it is much appreciated. Harry

 

Hi Darb, sorry I lost track of your thread...

Since those T T wires on the boiler control are low voltage, you can wire a simple switch to them and mount on the wall. Pretty much any type of switch will work, you can use regular thermostat wire to hook it up.

You can 'automate' the process by installing an aquastat on the incoming line from the woody and wiring it to these two terminals. Set for something around 140F and whenever the water from the woody is above this temperature the oil burner will be disabled.

To convert the aquastat to 'cold start', meaning that it will not fire up to keep the boiler at 125 (Low setting) when there is no call for heat, there is a simple completely reversible modification that you can do.

 

Another way to turn boiler into a cold start is to remove blue wire from spade B on right .

 

And as I've said before, this only does HALF the job, the CIRCULATOR is still under control of the Low limit when you do this.

The modification I've shown is the one that has been supported by Honeywell themselves, not some half job...

 

I do not understand how removing blue wire is a half job. The low limit will still keeps circulator pump off until boiler water temperature reaches low limit setting usually 140f. Thus preventing condensation inside boiler as its function when control is used with blue wire connected. What am I missing ?

 

What I think you are missing is that there is no point in holding the circulator off until 140, or whatever low limit setting you choose.

Holding the circulator off is not going to prevent condensation, and that is not the purpose or function of holding the circulator off during a low limit call.

The purpose and function of the hold off is to provide PRIORITY to the LOw Limit call when using a 'thankless coil' for domestic hot water to the home. By turning off the circ during Low limit call, all of the burner energy goes into satisfying that low limit call.

ALSO, when there is a Low Limit call in the absence of a heat call, you do NOT want the circulator to run and pump heat into the home, or in the event of a zoned system, into closed zone valves.

Holding off the circulator may in fact cause MORE stress to the boiler since when a heat call comes, the boiler will get to 140 (or whatever) and then when the pump kicks on massive amount of cool water comes back from the system... and hits that hot cast iron... and that's thermal stress.

If the pump is allowed to run at the start of a heat call without any hold off, the whole system warms at the same time with little thermal stress. The boiler is STILL going to get hot enough to dry out any condensation that occurs.

 

Hi NJ Trooper, thanks for the info. When warmer weather arrives I might try installing an aquastat on the supply line from the woody. With the circulators running more will this cause them to wear out quicker, and if so, would you recommend having a spare available in case one does stop working. Thanks Harry

 

Circulators are made to run. It's the stopping and starting that shortens the life.

 

Hello all! Saw this knowledge stream and had to join to tap into it. I just installed an outdoor boiler to my home heated with an oil boiler and three zones which are controlled by three thermostats and three circulation pumps.

I installed an aquastat on the boiler feed line going into a water-water heat exchanger which is located on the boiler outlet (too complex to install on inlet).

My boiler does not have TT terminals on the control, only the FF, no Jumper. The boiler has a domestic coil.

The burner is powered by a Honeywell L8124A,C Aquastat through the B1 B2 terminals. There is one zone in the house with a thermosat wire leading into the same controller, and the C1 C2 terminals control a circulator pump for the zone in question.

To install the aquastat I cut the B1 wire, ran it to the stat to intercept the signal as there are no TT terminals on by oil gun.

When the wood boiler comes up to temp, aquastat sees it (>120) and kills the power to the oil boiler, disabling it. Yeah! 2 zones which are controlled by an R845A and RA89A respectively work great.

Issue: When the strap on aquastat switch kills the oil boiler, it is also killing my circulator for that third zone. power is gone. I did not intercept the line voltage, it was the B1 terminal.

how should I wire this to resolve the issue of me losing my one circulator that is powered from the same Aquastat controller?

Thanks so much for the help.

 

Your 8124 is called a 'triple' aquastat. What HIGH, LOW, DIFF settings are you using?

I suspect that what you are seeing happening is that the aquastat is sensing boiler water below the LOW LIMIT setting and that is cutting off the pump.

That's what the 'triple' aquastats are designed to do... when boiler goes below LL, it implies that burners need to fire to bring boiler back up to temp in order to reheat the boiler and allow priority to the domestic hot water coil.

This brings up another question: How are you producing domestic hot water for the home? Is there a 'tankless coil' in the boiler for the purpose?

I would think so, because that's pretty much the only reason for having a 'triple aquastat' such as the 8124 installed.

Answers to these questions will probably bring some possible solutions.

The way you've got your system piped, it sounds as if the only time heat moves through the exchanger is when a zone is calling for heat.

A much better solution in my opinion is to set up what (I believe Central Boiler) calls a 'wrap around' pump.

This pump runs and circulates the water through the indoor boiler, keeping it hot all the time the woody is running, and essentially 'banking' heat in the boiler... similar to a buffer tank...

This wrap around pump and the heat exchanger would be on a separate loop around the oil boiler. The circulating zone water would not flow through this loop, but take it's normal route through the boiler and pick up the heated water already in the boiler, while the wrap around loop continuously 'recharges' it.

What is the make/model of the oil boiler?

 

Thanks for the reply,

I have a domestic coil in the oil boiler that I am not using. I use an electric hot water heater because the domestic coil was hot/cold. I might change that over if I find a good way to do it. right now the domestic coil is plumbed into the electric water heater outlet with a mixing valve. I figured it might make more sense to plumb it to the electric water heater inlet to use it as a "buffer" tank?

The boiler is a Burnham boiler, 4WFH. Beckett ignitor thing.

I checked just a bit ago and the internal boiler temp said it was about 165-170, warm from the return water coming back in. I would be surprised if that was "low enough" to trip the low limit, it's pretty warm because the pumps have been running nonstop to heat a slab floor. What do you think? That being said, when I turned the strap on up to enable the boiler it fired up right away so maybe its colder than I think.

I can take the strap-on aquastat and change the temp to kill the oil boiler, the instant the boiler stops the circulator pump dies, the instant it fires up the pump starts up again.

Give me troubleshooting ideas and I'll do em, got a multimeter and not afraid to use it.

You are correct, the only time the heat exchanger is really working is when the zone pumps are running. I just heard about the other way with a constant flow earlier, but I dont understand how to plumb that up. Got any diagrams? I hate to re-plumb after a tedious install, but I'm open to suggestions.

Settings:
Diff: 12
LO: 145
HI: 165

 

Just for ha-ha's... please take a close look and make sure that the circulator is in fact wired to C1 and C2. I know you have probably done this already, but humor me and look again please. Trace the wire from the pump back to the aquastat and make sure it doesn't make any 'stops' in between.

What you are saying can't be... it just doesn't make any logical sense at all... but then, who ever said boilers were logical?

Next, turn the LOW setting all the way down as far as it goes and see if that has any affect on circulator operation.

In the meantime, I'm going to study the 8124 schematic and see if I can come up with any possible scenario that this could happen.

Can you take a clear well lighted close photo of the interior of your aquastat?

 

Well, now I dont feel so bad if I stumped you. Before and after pics attached.



Its C1 and C2 for sure.

The "after" shows the green wire.

The wire to the circulator not working is the one that is not romex. I trimmed the B1 teminal coming from the oil boiler, wire nutted to black wire in a new romex cable, ran that to the strap on aquastat, brought the green wire back from the aquastat and into the B1.

ok.... update. You son of a gun. I turned the lo limit down to nothing and the pump kicked on. I am worried it is not a good solution long term, I don't want to push 120 degree water through the system. Suggestions?

 

HA! I've been called way worse!

That's not what will happen though...

How can I splane this...

The purpose of the Low limit is to disable the pump and fire the burner to maintain the boiler at a low limit setpoint and to provide 'priority' to this action such that the pump can't run. The purpose is for delivery of domestic hot water. So that when someone is showering if the heat kicks on, the shower doesn't go cold because cold water from a zone rushed in an cooled the boiler down.

When there is a HEAT CALL from the thermostat, that pump will run as long as the boiler temp is above the Low Limit setting.

There may be a couple things going on here:

If you've ever had the aquastat out for any reason, and when reinstalling it you didn't get the 'bulb' down to the bottom of the well, it will cause the bulb to think the boiler is cooler than it actually is.

This could also explain why the burner fired when you thought the boiler should be warm enough that it did not.

When setting the LOW and HIGH, it's very important that they never be set closer than 20F to each other. If you do set them closer, erratic and unpredictable circulator action can result because the two controls can 'overlap' each other.

Obviously, those dials are nowhere near what anyone would call 'precision settings'! So you may have had them just a smidge too close.

You said that you're not really using the tankless coil to heat your domestic, right?

You could modify the aquastat to completely eliminate the Low Limit control... then that pump would work just like the others, run whenever there's a heat call, regardless of the boiler temp.

 

Oh, one more thing...

GREEN is not really the best choice for a 120VAC HOT wire.

Sure, you know what it is... but think of that poor sap sometime in the future that knows GREEN is the color used for SAFETY GROUND wires.

Should be BLACK, or RED.

 

Ok, I am with you.

I might do this bypass mod you proposed, at least until i decide to use the domestic coil. What do you think about that coil feeding water to the electric water heater instead of bypassing the electric water heater like it is optional today?

I guess another solution or reduction of the problem would be to put in the heat loop you talked about. I figure if I put a T in the line at the heat exchanger outlet on the house side, run that to a circulator pump and T that into the return lines going into the boiler after the zone pumps I have the little pre-heater loop. Shoud I, could I set that circ. pump up to run only when the wood boiler aquastat is saying the temp is high? or just let it run?

so glad to sleep with all zones working tonight, you are the man.

 

oh, and i was limited to white or green cause i already used the black in the romex i used, and i wanted the green to be obvious (to me) which one I messed with. I'll put black electrical tape on it and will have new wiring diagrams with the boiler for the poor sole who tries to retrace my steps in the future.

 

Gettin' late here, gonna sack out.

I'll think more about this tomorrow...

Easy to get the pump to only run when woody is hot, but it might mean yet another relay to tie into the aquastat that turns off the burner.

That aquastat you used, does it have three terminals, R W B ? or just the two? What is the model number?

 

Hi again.

The Aquastat is I think an L6006A, it has the R, W, B terminals.

I did as you suggested and bypassed the low limit controller by connecting the two wires, and everything is functioning properly now. Lesson learned, thank you.

So, do you think I can use this to control a circulator pump for a small boiler warming loop? I dont want to burn crazy amounts of oil in case I let the wood fire die down. I know a switch would be simple to just disable the pump, but I like everything to be as hands free as possible.


the other question remains...
It seems to me I should again use the domestic coil in the boiler for free hot water, and again I am thinking I would take that hot water and feed it to my electric hot water heater to act as a reservoir to get more stable temperature and a buffer. Today I can choose between the electric water heat or turn it off (valve) and turn on (valve) the domestic, which goes to a mixing valve. I tried the domestic earlier and the water was hot-cold-cold-burning hot, so I switched back. This is a family of 5 with frequent overnight guests, so we go through some water for sure.

John

 

If you can pipe a loop around the boiler with the heat exchanger on it, you could theoretically use that aquastat to fire a relay, such as an SR501 (or equivalent, there are a few).

SR501-4 - Taco SR501-4 - 1 Zone Switching Relay

You could use one set of the relay contacts to turn the pump on, and another set of relay contacts to disable the oil burner.



When the woody is hot and the water comes up to temp, the R & B contacts close and trigger relay, the pump runs and the oil burner is disabled.

 

Wouldn't free be nice? Nothing is free, but I know what you mean.


To do what I think you are describing would take a bunch more piping...

You would need a BRONZE $$ circulator pump that circulated the boiler coil through the water heater, along with yet another relay to control it tied into the water heater controls...

 

I guess free is relative, the wood boiler was far from it that's for sure. but, I am in it for the long haul and should see a 3-4 year payback so I'm happy with that.

I had a different approach for the hot water.... what I am talking about is as you suggested putting in the loop to heat my oil boiler with the wood boiler all the time, and the oil boiler already has a domestic coil in it so I would be heating that domestic water coil with the wood boiler (right?) and would take the outlet of the domestic coil to the inlet of the electric water heater. Unless the water from the oil boiler wont heat the domestic coil for some reason, I don't know if that is a water-water heat exchanger or if it would be heated by the method I propose.

Then if I am heating my house with wood or oil, I would be heating hot water also and storing that in my electric hot water heater, taking a big burden off the heating elements by not having them heat up the supply water.

I can't find a reason not to do that unless the electric hot water heater would be damaged somehow from water too hot, that is why I propose a mixer valve to knock it down to 120 or so.

so, would you do it? would you add the extra loop? would you run it off the aquastat?

 

OK, but there would be no circulation from the coil in the boiler to the water heater if no water was being drawn from a tap.

So you wouldn't really be 'banking' hot water from the boiler coil in the water tank, only pre-heating the cold water going in.

Yes, that would probably mean cutting back greatly on the electric use, but there would still be some at times.

I don't see how the water heater could be harmed by feeding 130-140F preheated water in...

My idea I think you understood was to set up a 'recirc loop' between the water heater and the boiler coil with a pump.

There are systems called 'aqua-booster' that do just that, but don't actually have their own heating elements, they are only storage tanks. There's a pump in line between the boiler coil and the tank and when the tank calls for heat it runs the pump.

If it were mine, yes, I believe I would. Yes, I would probably do something along the lines of the Taco relay and the aquastat.

You will need a properly placed flow check valve (maybe two) so that the loop only circulates through the boiler and not pull from the system piping.

Here's something at Central Boiler website:

http://www.centralboiler.com/Tech/C220.pdf

What I don't like about that setup is that there will always be some circulation through the baseboard heat unless there are zone valve in the way.

Also, when the central heating pump runs, some of the flow will bypass the boiler through the wrap around loop, which isn't a problem as long as there's a fire in the woody. Even if the woody is cold, having a boiler bypass loop isn't really a bad thing either.

The way that drawing is shown, there's no place to put a check valve that would work.

You might consider using a shell and tube heat exchanger on the water heater... maybe even in addition to plumbing the coil in the boiler to the water heater inlet.

 

That central boiler diagram confuses me with the water heater. They have a tube in tube exchanger on the water heater but are relying only on convective heat transfer to heat the water in the water heater? the supply to the water heater and the outlet neither pass through the heat exchanger, it is not a forced convection. seems pretty stupid to me, that heat exchanger should be on the "cold" line.

and yes, my suggestion would only work to pre-heat ingoing water, but I have the domestic coil already installed so, why not I guess. I dont see buying another heat exchanger to do the job. Like you said, maintaining tank temp would still be done with electricity, but I think the bigger battle is getting the cold water warm in the first place, at least in the heavy use household I have.

I think the loop they have would work, don't the circulation pumps act somewhat like a check valve? they are at least a good restriction, I don't know if they let much flow go through when they are not moving. Today I have three zones all "T"d together next to each other on my heating system return lines and I don't get backflow or suction through the non-engaged pumps. The pipes on the dead lines are very cold even though they are very close to a running pump connected right next to it. So, I could set up a fourth pump with the little loop as shown and it would be identical to a 4th zone being added to my system.

I am going to do this if I can get a pump cheap enough. I like keeping the boiler warm all the time so condensation, etc. doesn't get me- and so I can pre-heat my domestic hot water supply even if the house isn't calling for any heat.

Thanks again for all the help, I will pass this knowledge on if I get the chance, my boiler sales rep was not up to the task on this one.

 

I just installed a Central Boiler to an existing hot water system and have control questions too, so this seems like a good thread to comment on. I have a comment or two about application to domestic, so I suppose that will be first.

Central Boiler provides quite a bit of info and diagrams with the manual and such. I think they want their boilers to maintain 185 F to prevent condensation and corrosion, so everything else seems to be designed to use that temperature. I am not a fan of maintaining 185 F with a hot water tank, but it will provide an ample supply of hot water if used with a mixing valve. I may go that route myself...my domestic is currently still electric. The thermosyphon (or whatever) provided with a tube in tube exchanger should work fine considering you have an entire tank at 185 F and mix it to a usable temperature with a mixer valve.

My Central Boiler feeds a 1 zone Eshland wood/oil boiler in my basement. That unit feeds hot water to cast iron radiators on two stories in a very drafty old house. The chimney on the basement stove is bad, so I don't burn wood there and the oil burner has been totally disconnected from the controls. The Central Boiler is the only heat source. It is plumbed directly into the inside boiler. The supply is tee'd into the drain on the bottom and the return is tee'd onto the pressure relief on the top. The controller is a Honeywell, similar to the L8124A, but I am not sure of the model as the sticker is missing from the cover. I saw an L8124 on a youtube video and mine looks to be identical.

My issue is the circulator and temperature. Central Boiler require all installs to use a supplied valve placed before the inside furnace that will mostly bypass the inside distribution and return the 185 F water to the outside boiler if the return temp from the inside unit is less than 150 F. You only get a portion of the 185 F from the outside boiler until the return temperature is over 150 F. The controller doesn't seem to want to send heat to the radiators unless the low control knob is set to about 130 F. I think I need that to maintain above 150 to get the full flow from the outside boiler. I am not sure if the aquastat is faulty, or if I am missing something. None of the jumpers have been removed. When I set the low to 150-160 and the high to 185-190, the circulator isn't sending water when the thermostat calls for heat. If I turn the low control down to about 130 F, the circulator kicks right on.

I have no current plans to use an oil burner, so I rely solely on the outside wood boiler. I think I need the circulator to send with a low temp of no lower than 150 F to facilitate full flow and quick recovery from the outside unit. How can I make that happen? Could the current Honeywell be faulty?

 

And in fact 185F could be damaging to an electric water heater. I don't know this for a hard fact, but I seem to recall having read it somewhere... do your homework on this and look at the specs for your water heater to determine if they spec an upper limit water temperature... maybe even call the manufacturer (good luck with that! )

Trying to visualize your setup...

So the return from the radiators comes into a tee, the hot supply from the woody comes into that same tee, then into the boiler?

Where is the circulator pump for the home in relation to this connection?

You've pulled the pressure relief, added a tee in between it and the boiler, and the return to the woody comes off this tee?

Right... a thermostatic bypass valve that allows the woody to run at temperature...

There's no problem with this part of the install, correct? Only informational?

What should happen is that as long as the woody is at temperature, that valve should be open, and based on how I believe you have this setup, the indoor boiler will eventually come up to 185F also because when the thermostatic valve opens, the woody water will circulate through the indoor boiler.

Does that happen?

That sounds like normal operation of a 'triple aquastat' like the 8124 (and others).

When the controller senses that the boiler water temperature is TEN DEGREES BELOW the setpoint, it will DISABLE the circulator in order that the boiler can recover.

If your system is connected as I think it is, that should not be a problem because the indoor boiler should be up at the 185F setpoint of the woody and the circulator should run...

Would it be possible for you to post a diagram of the hookup, showing the location of the circulator for the indoor boiler? Doesn't have to be elaborate, as long as it's accurate...

 

The Eshland in the basement is a cube shaped (sort of rectangular, actually) firebox with @ 3-4 inches of water jacket surrounding the firebox all the way around. the drain for that boiler is in the bottom left. The pressure relief is in the top right. the supply from the outdoor boiler is tee'd to the drain and the return to the outdoor boiler is tee'd to the pressure relief. The once pressurized indoor system is now sharing water with the open outdoor system.

The Eshland indoors supply and return to the radiators are totally separate ports. The return from the radiators is in the bottom middle and the supply to the radiators is in the top middle. These are large ports...looking to be 1.5 or 2 inch reduced to 1.25. Unfortunately, the circulator pump is currently located, old school style, on the return from radiators and not the supply like it should be. That will hopefully be changed next season. It just cannot happen this winter.

This was the first day of operation. The house is warm so far even though I had the thermostat set at 75 and it seems to be maintaining 70-72 in the room with the thermostat. I fear that if the need for heat as winter gets hard increases, it will slow the supply due to the 150 F return to outside valve slowing the recovery. However, I suppose I need more data and observation to see what is actually happening vs. what I think I need to have happen. Like I said before, I think I need to have the circulator stop circulating if the indoor boiler temperature drops below 150 F as this will restrict the outdoor supply to a trickle due to the Central Boiler bypass valve that doesn't want water lower than 150 F returning to the outside boiler.

 

OK, I think I get it now, thanks for the further explanation!

If you're not running a pressurized system, I don't think I see where that matters much...

This does bring other issues though.

First, you will now be pumping OXYGENATED WATER through all that cast iron and whatever other ferrous metals are in the system

This is bad... think CORROSION (RUST)

For ferrous metals to corrode, three things are required.

1. Ferrous metal

2. Water

3. OXYGEN

Take away any one of the triad and corrosion can't occur.

Pressurized hydronic systems have little to no oxygen in them after the water is heated a number of times and the water becomes basically INERT. No (little) corrosion.

If you're running straight water, you are going to have problems... expensive problems.

Next, if the radiators are above the height of the wood boiler, a VACUUM (less than atmospheric pressure) will form in the parts of the system that are above the level of the wood boiler.

This vacuum is going to 'pull' the air out of the water and will form bubbles that will block the flow of water.

Third, circulating pumps in CLOSED and pressurized systems don't need to overcome the 'head' that a height difference will add to the system. In a closed system they don't need to pump the water UP, they only need to pump the water AROUND, like a Ferris Wheel of Water.

In an OPEN system, the height ADDS LOAD to the pump. Your existing pump may not be completely up to the task.

It's not TRULY an open system though... because you aren't discharging to a higher elevation, but there may be SOME extra load on the pump.

(never mind that the pump is probably cast iron and will rust quickly, along with the rest of the ferrous metal in the system)

If I were you I would STRONLY consider re-doing that system and using a flat plate heat exchanger to keep the home side pressurized and oxygen free.

I don't see any reason that you need to keep the triple aquastat at 150. Let the water circulate... turn the low setting down to say 130 and let the thermostatic valve to do it's job.