L8124A is it functioning as designed?

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Old 12-01-10, 11:28 AM
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L8124A is it functioning as designed?

Hi,

I have a L8124A aquastat and something about this device has always troubled me, I'll try to explain:

The home has 2 types of heat:
- Radiant which only needs 120deg to run, this system for the most part runs all the time. It has a mixing valve to accomplish the 120deg floor feed temps.
- We also have 3 zones baseboard heat, runs mostly on very cold days.
- Also have another zone for heat transfer tank for hot water, simply another zone.

The goal for using the L8124A Aguastat was to set the lo-limit to 150deg and the differential to 20deg this easily can accommodate the radiant heat by just using the ability of the aguastat to maintain boiler water temp in the range of 140-160deg. My understanding is that if the lo-limit is set to 150 and the dif to 20 then with no call for heat (from the baseboard or hotwater zones) the burner comes on at 140 and shuts off at 160. The radiant system simply gets hot water (if needed) from the boiler without ever calling for heat. I like this setup so far as it allows the boiler to run at lower temps if only the radiant is running. This all works great.

Here's the bad part:
When the baseboard or hot water tank call for heat then the aquastat sees the call for heat and the hi-limit now is in play. The high limit is set to 190F (to achieve long cycle run times). Let's say boiler temp is at 150F, burner off, radiant running and we get a call for heat from a baseboard zone that's stone cold. Then Circulator comes on, moments later burner comes on because we are now honoring the hi-limit of 190F but all the cold water from the baseboard is rushing into the boiler and the boiler instantly starts to cool down even though burner is on. Next it cools to the 140F (150F Lo-limit minus 10F=140F) now the circulator is shut off as it should be. Next the water temps start to rise and at 160F (140F+diff of 20F = 160F) the circulator comes on as should be. Then the problem starts, as soon as circulator comes on the burner immediately shuts off? Almost like the system forget there's a call for heat. Then within 10 seconds burner comes back on as if it suddenly remembered the call for heat and the burner now remains on till the 190F is reached. So long as call for heat remains everything else is perfect.

The trouble spot in the above scenario is that 10 second pause in the burner as we transition from lo-limit temps to hi-limit temps during warm up on call for heat. I'm trying to optimize for long burner run times and this 10 second burner off-on is bad.

I suspect the issue has to do with the fact that the lo-limit high side is 160F while the hi-limits lo-side is 180F so we have a 20deg gap between the bottom of the hi-limit range and the top of the lo-limit range. Just a theory.

Any thoughts?

Thanks.
 

Last edited by scarceller; 12-01-10 at 11:57 AM.
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Old 12-01-10, 05:04 PM
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My understanding is that if the lo-limit is set to 150 and the dif to 20 then with no call for heat (from the baseboard or hotwater zones) the burner comes on at 140 and shuts off at 160.
Correct understanding.

My presumptions about your system, based on your description, please correct if wrong:

You have separate thermostats for the radiant and the baseboard. Yes/No

The radiant thermostat only controls a circulator dedicated to the radiant portion. You said that it does not generate a call for heat so this must be so?

Thermostat for the baseboards is what calls the boiler for heat, this I understand, but I'm presuming that the baseboard is on it's own circ. Yes/No

Then the problem starts, as soon as circulator comes on the burner immediately shuts off? Almost like the system forget there's a call for heat.
I have no good explanation for this behavior. It shouldn't happen. When there is a heat call, the aquastat relay pulls in (1K1 in the schematic if you are following along in the Libretto) and that relay REMAINS pulled in when the boiler cools to LOW limit. It remains pulled in for the duration of the heat call, whether or not the boiler cools and the LOW limit / circulator control is activated. When the boiler temp hits 160 and the Low limit control switches, the burner should remain energized...

Do you have a multimeter and know how to use it? If so, set it up for 120VAC and clip onto B1 and B2. Watch carefully to see if the burner voltage drops out momentarily. A digital meter may or may not 'catch' the event. An analog meter would be preferred for this... but if it drops out long enough, you might catch the event on a digital.

I'm wondering if there's a crappy solder connection that 'blips' when the switch 'flips'...
 
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Old 12-01-10, 05:06 PM
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suspect the issue has to do with the fact that the lo-limit high side is 160F while the hi-limits lo-side is 180F so we have a 20deg gap
I don't think so... that shouldn't cause your symptoms.
 
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Old 12-01-10, 05:13 PM
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I want to give a few of my thoughts on your system:

You push the high limit up to 190 to achieve longer cycles. To what end? If the purpose is to get long cycles so as to maximize efficiency, you are very likely eating up any efficiency gains with the higher temperature. And that higher temperature is very likely not needed to heat your home. I would set it back to 180.

You are running the boiler warm start... keeping it warm 24/7. To what end? It's a waste of energy. Keeping that boiler warm 24/7 during the heating season is costing you a bundle...

You've already got the mixing valve for the radiant, and a circ for the radiant, so why not set the boiler up for cold start and simply let the radiant call the boiler and only heat up when needed? Just like your baseboard and water heater zones do...

I just can't see the logic behind it...
 
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Old 12-01-10, 05:19 PM
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The 3 baseboard thermostats call for heat via the T-T terminals and all 3 of these zones share one circulator on the return

The radiant has separate thermostat and circulator on the feed, this system is not wired to call for heat since temps are so low at 120F no need to call for heat, it simply draws water from boiler as needed via a mixing valve set to 120F.

The 3rd system is a hot water transfer tank on it's own zone with it's own circulator, this system does call for heat and is also wired for priority so that if hot water calls all other systems shut down.

Then for the issue at hand:
I'm an electronic engineer and have plenty of good equipment, DVM and scopes.
I'm glad to here that I'm not nutts and that this really should not be happening. What I know is it seems related to exactly when the circulator is commanded back on once lo-setting temp comes back up to 160F at the exact moment I see the circulator relay pick the burner cuts out. I'm now starting to suspect something may be occurring on the TT (thermostat) lines. Maybe I'm dropping 24V here, this would certainly cause the issue I describe.
Bottom line is you are saying that if burner is running and we have solid call for heat (TT active) the burner should never cut out till hi-limit of 190F is reached. This is good to know and I think I can diagnose from here. I'm going to look very closely at the TT line to see if something is happening on it when circulator is commanded back on.

Thanks.
 
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Old 12-01-10, 05:22 PM
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Radiant which only needs 120deg to run, this system for the most part runs all the time
OK, maybe there is some logic to this... IF the radiant does in fact run all the time. In that case, it might make sense to keep the boiler warm in the way that you do. BUT, in this case, I might consider even dropping the LOW limit another 10° or so. If your mixing valve is at 120 (which seems a bit on the high side to me by the way...) then why can't you lower the boiler temp a bit? It will save you a few bucks.
 
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Old 12-01-10, 05:29 PM
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This entire system is a pet project of mine and you may very well be correct that 190F is simply to high I can easily drop to 180F with no issue.

As for cold start setup: would this effect my hot water? I have Amtrol hot water exchanger so I suspect even a cold start setup would work fine here, especially during the Summer.

The next thing I'm working on is installing a IntelliCon HW Plus 3250 to really achieve long run cycles. What I'm not sure about is should I keep the current L8124 aguastat? The real reason I choice this aguastat was so that boiler had two set points one at about 150F for radiant which is what runs 100% during winter and the other at 180F for when baseboards kick in on real cold days. That was my original thinking but maybe this just really doen't matter and I should just always run at 180F hi-limit with cold start?

I'm open to suggestions to make a more efficient oil system with what I have. Boiler is SlatFin 4 years old in great shape I do not wish to replace it.
 
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Old 12-01-10, 05:33 PM
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I can easily also drop lo-set to 130F but I did not do this because I had been adviced about condensation on the boiler it self with temps near 120F. Any truth to this?
 
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Old 12-01-10, 05:33 PM
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I'm now starting to suspect something may be occurring on the TT (thermostat) lines. Maybe I'm dropping 24V here
OK, a little more explanation about the burner control then... if you take a look at the schematic for the 8124A, you will see the LL/CIRC control. When the temp drops to 140, that control 'makes' the R-B contacts, at the same time it 'breaks' the R-W contact. This is what disables the circ when the temp dips... as it should.

During a heat call though, keep in mind that 1K1 is always pulled in, and when the temp drops to 140 and R-B 'makes', all it is doing is shunting (paralleling) 1K1 with another pair of contacts.

I don't see how the 24 V could be dropping. That's coming from the transformer in the aquastat which has a constant 120VAC on the primary.

If you don't see anything on the meter on B1 and B2, get adventurous and hook up the scope... it would be nice if there was a way to trigger the scope to catch the dropout, but with an AC signal it might be tricky... you might have to set the horizontal to a slow trace and just sit and watch it... (you can talk EE mumbo-jumbo with me, no problem)

Maybe a Dranetz power analyzer would be a better choice... you can just set it up to trigger on an exception and walk away.
 
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Old 12-01-10, 05:41 PM
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I have to go back and re-visit my baseboard heat thermostat wiring, as I recall I did this in a very different approach to wire 3 thermostats into the TT line (don't ask, I sometimes do crazy stuff. It's the EE in me). I could have easily screwed something up here, I'm going back to my wiring diagrams from 3 years ago to re-visit the setup.

I'll let you know what I find.

I still could use advice on the Heat Manager control I just bought. I have no problem wiring it up I'm just curious if it would work better with some other aguastat.
 
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Old 12-01-10, 05:48 PM
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My opinion in case you ask... forget about the Intellicon... do a search in this forum and you will find a very long and interesting debate about that thing... including some comments from it's 'inventor'...

I've gotta head out for a while, but I would like to address some of the issues you raised with condensation, etc,,, interesting topic... 'Boiler as Hobby' ... one of my favorites!
 
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Old 12-01-10, 06:11 PM
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What I have yet to say is that the 3 baseboard zones share 1 common circulator on the return controlled by aquastat but each zone has a zone valve, all 3 zone valves have dedicated transformer (not the 24V one in the aquastat) then the 3 thermostats for the these zones simply are wired to the zone valves (Honey Well ball valves). So the thermostats simply command a zone valve open or closed. Then the end-switch in each zone valve are all wired in parallel to the TT on the aquastat, so if any end switch closes on a zone valve (1 or more close) it shorts the TT terminals. But the interesting thing is that the 2 transformer grounds (white wires) are now connected together, since the dedicated external transformer runs the zone valves and thermostats while the other aguastat internal transformer applies power to one end of the end-switch in the zone valve. I can easily see a ground loop between these 2 transformers. I'm going to try a test where I manually (by hand) open a zone (this does not close the end-switch) then I'll disconnect wires from the TT terminals and jump the terminals by hand and see if this fixes the issue. If the problem goes away then I know what area needs re-thinking.

I just knew I did something wacky in how I wired the TT terminals, The thermostats don't directly wire to TT the zone valves do.

I'd love to hear more on the IntelliCon HW Plus 3250, I bought this thing cheap at $130.00 and saw many folks saying it helps and saves money.

Calling it a night for now.
Thanks for the help

I also will call it a night.
 
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Old 12-01-10, 07:34 PM
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As for cold start setup: would this effect my hot water?
To a limited extent, yes... but you may not have a problem with that extent. What will be affected is the 'recovery time'. There would be a short period of time as the boiler water heats up before it's above the temp of the water in the tank, and contributing it's heat to the domestic water. On the flip side, keeping the boiler warm start, as soon as the water heater calls, the warm water in the boiler immediately starts doing it's job. If the water heater is large enough, the short lag time while the boiler gets up to temp might not even be noticed. The generally accepted term for your type of water heater is an "Indirect Water Heater".

I can easily also drop lo-set to 130F but I did not do this because I had been adviced about condensation on the boiler it self with temps near 120F. Any truth to this?
I've highlighted 'ON' in your quote, the condensation occurs IN the boiler itself, on the fire side of the heat exchanger, and also in the chimney.

Yes, and no. The condensation that you are talking about is 'flue gas condensation'. The 'dew point' of flue gases in an oil fired system is supposedly 113°, and in gas fired appx 132°. I'm not comfortable with the 113° number myself, but not for any scientific reason, just a gut feeling that the number is too low. A well respected author (John Siegenthaler) in his book "Modern Hydronics" says that oil fired flue gas dew point is 150°. I have not studied the chemistry in detail, but my belief is that gas fired flue gases are more humid than oil fired... so oil dew point HAS to be lower... in this, and ONLY this, I think I have to disagree with Siggy... I've seen too many OTHER citations that say 113...

The 'tune' of the oil burner also affects the dew point. Typically, burners are set up in such a way that there is around 40-50% excess air. The higher the excess air, the lower the dew point.

BUT... there is also an ACID DEW POINT, and that point is directly related to the amount of Sulfur in the fuel, and this sulfur could raise the dew point. It's very possible that Siggy is referring to the ACID dew point, and he's smarter than I, so is probably correct... I'm not about to brush up on Molar Analysis to prove any points though, and I digress, badly.

I'm going to use 125 for oil, and 135 for gas.

What this means to us is that whenever these gases are in contact with a surface below the dew point, condensation occurs, and that condensate is acidic due to the nature of the chemical process.

In general, the condensate problem only occurs when there is a LARGE VOLUME of COOL RETURN WATER coming back to the boiler during a firing cycle. This cool water will in turn cool the steel or cast iron surfaces on the FIRE SIDE to the point that the water vapor will condense.

SOME CONDENSATION OCCURS in EVERY boiler at some point in time, there is no avoiding that. If it occurs for short periods of time, it's not a problem because as the boiler continues to heat, it is dried up and gone. In the absence of the water, no corrosion can occur... it's the LONG TERM condensation that is a known problem.

I'm sure you could safely drop your low limit down to at least 140, maybe even 135 (or ignoring safety margins even lower). The burner would still fire (using your 20° diff setting) when the boiler cooled to 125-130... ABOVE the dewpoint still... no problem.

Next, we'll talk about what happens after the flue gases leave the boiler and into the chimney because the flue gases can also condense there... since the average temp of the boiler is cooler, the flue gas TEMPERATURE will also be lower. This of course means that the chimney temp will be lower. If any part of the chimney drops below the dew point, you will have condensation occur at that point. Generally not a problem for a manufactured double wall insulated chimney that is enclosed most of the way to the top, but if you happen to have a cavernous tile lined chimney on the outside wall of your home, it's very possible for condensation to occur there as well. So, the flue gases have to keep the chimney warm enough, all the way to the top.

Good Lawd... I am hopeless... I hope you've read this far!
 
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Old 12-01-10, 07:59 PM
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curious if it would work better with some other aguastat.
No, aquastat won't make any difference.

I know that there have been some firmware changes incorporated into the product in the couple years since I've had one connected to my system for evaluation (which was removed because it didn't do anything), but IN GENERAL what the HM does is INCREASE THE DIFFERENTIAL of the aquastat. It supposedly does this by measuring the 'rate of change' of the supply side water out of the boiler AFTER THE BOILER HAS HIT IT's HIGH LIMIT.

On my system the boiler almost NEVER hits high limit, and my HM almost NEVER 'economized'. My home is 'over radiated' to a degree, and even when it's like 0° outdoors, my water temp rarely gets over 160°.

Your mileage may vary, but I was not impressed. Use the search function to see if you can find that thread... it was about a year or two ago.
 
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Old 12-01-10, 08:10 PM
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I just knew I did something wacky in how I wired the TT terminals, The thermostats don't directly wire to TT the zone valves do.
You didn't do anything wacky at all. That is absolutely the normal, standard way to wire zone valves.

Thermostat switches 24VAC from external transformer to MOTOR in zone valve on or off.

Endswitches in parallel to TT on aquastat.

While some zone valves do in fact have a 'common' connection, and ONE SIDE of each transformer is wired together as you describe, there is NO PROBLEM with that. Both secondaries are ISOLATED from line, and there can be no interaction when only one side is common. There is no 'complete' circuit to interact with each other.

You said "Honeywell ball valves" ... if by this you mean the V8043 series of valves, there is NO electrical connection between the motor circuit and the endswitch. In these valves the endswitch is a simple 'MicroSwitch' that is DRY... totally isolated contacts.
 
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Old 12-02-10, 05:20 AM
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Trooper, I found my problem! As I suspected I was to clever for my own good, I'll explain:

The Aguastat has 2 other terminals I'm making use of:
- ZR, this one is used to activate hi-side limit and I use it if my Amtrol heat exchanger calls for heat. No problems here working just fine.
- ZC, this has 120V on it so long as I'm above the lower lo-limit 140F (150F-10F) then if the boiler goes very cold (below 140F) because of in rush of cold water this line goes to 0V. So in my clever thinking I figured why not use this ZC line to power all the trigger devices so no zone could ever possibly call for heat if boiler drops below 140F. This ZC line feeds the following devices:
1. The actual main power to the Amtrol, this way amtrol can never call for heat if the 140F limit is violated
2. The radiant heat circulator, same here: shuts down radiant zone on violation of 140F limit
3. This ones the issue! I also power the external transformer for the zone valves from ZC and that's the problem! When we drop below the 140F limit the ZC goes to 0v and this causes the transformer to loose power and all baseboard zone valve close! and TT looses it's contact! then boiler comes up to 160F (140F + 20Fdiff) and baseboard circulator kicks back in and the transformer gets power once again but it's to late! The TT contacts have been broken earlier by trans loosing power so even though we are transitioning back through 160F we really don't have a call for heat till that trans gets it's power back. This is the cause of the burner shutdown then immediately back on again!

This was easy to figure out once I did my manual test where I forcefully kept TT closes with test lead and saw the problem went away. This then told me what to look at, obviously something was going on with the Baseboard zone valves.

There's a little bit more to the issue since the Amtrol is also wired priority. But in the end the issue simply is that the transformer for the Baseboard Zones looses power when boiler temps drop below 140F.

My system wiring is really not that simple but other than this small issue it works great.

This setup allows me to be certain that no zone will ever draw water if temps drop below 140F this includes the Amtrol water exchanger which always was my goal.

I'm revisiting how I provide power to the external transformer but I can't simply hot wire it to 120V because this would then break my priority wiring for my Amtrol. I'll think of something I'm sure.

I'm so thankful I created a wiring diagram 3 years ago!

Thanks for your guidance and support it certainly helped my diagnose my issue.
 

Last edited by scarceller; 12-02-10 at 07:51 AM.
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Old 12-02-10, 10:45 AM
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Trooper,

First be sure to read my prior post #16

I have a new circuit/wiring solution to my problem, I'm going to use this little device to help cut power to base board zones on Amtrol call for heat (priority to water heat).
Amazon.com: Zettler Miniature Power Relay 30A SPDT 120VAC AZ2280-1C-120A: Home Improvement
This is simple SPDT relay activated via a 120v coil (not 24v).

I can't figure out if you can post pictures on this forum? I don't see how. If you send me a private message with an email id I'd be happy to share my old and new circuit wiring diagrams.

I'm rather confident my new circuit will provide exactly what I need. The goal of my setup is as follows:
* 2 diffrent setpoints
- 140F lo-limit with diff of 20-25F for boiler water temp maintain, always have the boiler at this temp when no call for heat. The radiant heat system uses boiler water in this mode, it never calls for heat. I may lower this setting to 130F in the future. Radiant only runs at 120F
- 180F hi-limit, this is when Amtrol Hot Water Zone or Baseboard zones call for heat.
* Priority to the Amtrol zone always, if Amtrol calls for hot water then all other zones are shutdown
* If boiler water temps drop below the low level set point 130F (140F-10F) then every zone shuts down till boiler comes up to the lo-limit high point of 150F (130F+20F). I like this idea to give the boiler a chance to recover from very cold conditions on in-rush of cold water.

I think my new circuit meets all these needs and no longer has the burner 10second kick out issue.

Now I'm ready to install the INTELLICON HW+3250 device. I do agree with you that this device seems to simply widen the diff window on the hi-limit with some sort of special algorithms. It's easy enough to wire up so I'm willing to try it out now that my other issue is resolved. But the question is: does this device really have any benefit over a aguastat that has the hi-limit diff set at more than 10F? Of course my L8124 does not have adjustable hi-limit diff, it's always 10F. Anyway I'm willing to try it.
 
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Old 12-03-10, 03:47 PM
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Dangit! I hate what that happens! I just had almost finished my reply and lost it... now I gotta start all over...

To post pics, you need to first upload to a picture hosting site like Image hosting, free photo sharing & video sharing at Photobucket (free account) and come back here and provide a link to the album.

I fully understand the problem you found... good work! I'm reviewing the schematics that you sent... I might have some comments... but maybe not!

If the HW works for your application, great! if not, check out the Honeywell L7224U ... it is field configurable to replace single and triple aquastats, and has adjustable diff on both the high and low limits.

Product
 
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