"Modifed" Wiring on L8124A, C L8151A Triple Aquastat

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  #1  
Old 11-20-14, 11:57 AM
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"Modifed" Wiring on L8124A, C L8151A Triple Aquastat

Trying to understand the wiring on my aquastat - simple single zone setup... wiring doesn't match what I would think it would, and there is an another device on the flue that I am not familiar with... In addition, the cover has "MODIFIED 11/9/92" written on the schematic (but the schematic was not revised)...

Trying to understand how this is all connected and operates, so I can connect a new 'smart' thermostat...

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Old 11-20-14, 04:19 PM
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wiring doesn't match what I would think it would
How do you think it should be? What are you comparing to?

there is an another device on the flue that I am not familiar with
Is that what's in the second photo? Can you pull back with the camera some and get some more light down there and take some more pics?

Show us ALL the controls on the boiler.

Tell us the make and model of the boiler.
 
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Old 11-20-14, 04:45 PM
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OK, I can see one 'modification' in the wiring.

That red wire that comes from L1 and joins to the Black that goes out (presumably until I see more, wider angle photos) to the burner is also joined with a red wire to the "ZC" terminal.

What that connection to the ZC terminal is doing is BYPASSING the Low Limit circulator control.

The Low Limit BURNER control is still in effect though.

Does your boiler also provide domestic hot water via a coil inside the boiler or do you have a stand alone water heater?

Do you know of any other reason that the boiler should be kept hot at 160F 24/7 ?

What is that other (fatter) white wire coming up with the BLK, RED, YEL, WHT from that connector? Where is it going to, coming from?
 
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Old 11-20-14, 04:48 PM
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Trying to understand how this is all connected and operates, so I can connect a new 'smart' thermostat...
I can help you understand the existing wiring, but the bad news is that if your new thermostat needs a "C" (common) wire, there is no place to get it from on that aquastat control.

There are options of course...

Will your new thermostat be operating the HEAT ONLY?
 
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Old 11-20-14, 08:19 PM
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Tell us the make and model of the boiler
American-Standard Arcoliner Model 0154T 2BT J3 Series

Beckett burner

How do you think it should be? What are you comparing to?
Wiring schematic on the inside cover - for instance, nothing on B2...

Is that what's in the second photo?
May be an oil vent damper? Learning this as I go, but would make sense since it's on the flue...

Show us ALL the controls on the boiler.
No other controls - just the aquastat and the ovd (and burner and circ)

What that connection to the ZC terminal is doing is BYPASSING the Low Limit circulator control.
Does your boiler also provide domestic hot water via a coil inside the boiler or do you have a stand alone water heater?
Provides DHW... so still get low-limit boiler control for dhw; what is the reason for bypassing low-limit circ control?

What is that other (fatter) white wire coming up with the BLK, RED, YEL, WHT from that connector?
Sorry bad pic, it's not connected

but the bad news is that if your new thermostat needs a "C" (common) wire
Yea, no "C" wire is exactly what I thought and was looking for... what's the solution?

Will your new thermostat be operating the HEAT ONLY?
Yes, no A/C


Can upload more pics tomorrow with wider angles...

Thanks...
 
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Old 11-21-14, 12:12 PM
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Additional pics:

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Don't think this is a damper...

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Old 11-21-14, 04:55 PM
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schematic on the inside cover - for instance, nothing on B2..
B2 is the 'neutral' connection for the burner. If it's working it simply means that the burner is picking up it's neutral connection from another source. Not an issue...

May be an oil vent damper?...

Don't think this is a damper...
No, you're right, it's not a damper. It's what is called a 'stack switch', but it's old enough that I'm not familiar with that type.

This is what oil burners used before they used 'cad cells' to prove the flame.

Modern burners have a 'cad cell' inside the tube that 'sees' the flame. When a cad cell is dark, it's resistance is very high. When it sees light, the resistance drops dramatically.

The modern oil burner 'primary control' uses the resistance of the cad cell to tell if the flame is lit or not.

The older style 'stack switches' had a bimetal element inserted into the flue pipe that sensed HEAT.

If the system called for heat and the burner didn't fire for some reason, the stack switch would not sense heat in a set amount of time (45 seconds give or take) it would kick the burner off and lock out.

Cad cell is MUCH more reliable. Doesn't have to wait for heat to build, and is not an electromechanical nightmare relying on springs and paper clips in a snap trap mechanism that gets hit with flue gas and crazy temperature swings.

Your system COULD be retrofitted with a CAD cell setup... but it would cost a few bucks to do so.
 
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Old 11-21-14, 05:02 PM
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Provides DHW... so still get low-limit boiler control for dhw; what is the reason for bypassing low-limit circ control?
Well... I can't really say what their logic was for that.

The way a triple aquastat (what you have) is supposed to work on a boiler that provides DHW to the home is this:

When the boiler falls 10F below the LOW setting, the burner fires to heat the water back up to the setpoint. (actually the temperature that the burner stops firing is [ ( LOW - 10 ) + DIFF ] )

At the time the burner is firing on LOW limit, the circulator is typically DISABLED. This is so that the burner can give full power to reheating the boiler for the DHW use and not have to ALSO heat the home.

Perhaps the person that modified that wiring thought that the burner was big enough to heat the DHW AND the home at the same time... maybe it is!

That's my best guess.

I think it's also possible that there may be a problem with the aquastat. Maybe that part stopped working properly so they just bypassed it. Whoever did it did a reasonably good job. I don't think that's a homeowner modification.
 
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Old 11-21-14, 05:16 PM
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Yea, no "C" wire is exactly what I thought and was looking for... what's the solution?
There's a few possibilities.

1. Replace the aquastat with a model that has the "C" wire available. $$$$$$

2. ADD a relay such as an SR501 in between the thermosat and the aquastat. $$

3. ADD a 24VAC transformer and (hopefully) get it wired properly so that you don't burn out the transformer in the aquastat or your new thermostat. $$ if you're lucky and careful or $$$$$$$$$$ if you're not either.

4. Use a 24VAC 'plug in wall wart' to power the thermostat. Same precautions as above.

Being able to properly perform either 3 or 4 above means that you would have to know exactly which "T" terminal on the aquastat is which in terms of the internal wiring.

The wall wart solution is the easiest and potentially least costly. You would need an outlet nearby to plug in the wart. I think we can figure out which wire goes where on the " T T " terminals on the aquastat.
 
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Old 11-21-14, 05:19 PM
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By the way...

Is your hot water from the taps REALLY REALLY HOT?

Does anyone in the house ever get scalding burns from the hot tap water?

Do you know if there's a 'thermostatic mixing valve' on the hot water piping coming off the boiler and going to the home?

Are there children or elderly persons in your home who are at higher risk of scalding burns?
 
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Old 11-21-14, 06:28 PM
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Your system COULD be retrofitted with a CAD cell setup... but it would cost a few bucks to do so.
So the stack switch is basically a lock-out in case there's a problem with the burner... makes sense and no reason to replace (been working since '56 or whenever).

Perhaps the person that modified that wiring thought that the burner was big enough to heat the DHW AND the home at the same time...
House is abt 1600 ft2 (1000 1st, 600 2nd) with Sunrad recessed radiators... May explain why, if the timing is right, there is no DHW (i.e. shower) if the heat just kicked on, right?... no big deal, though, and again, working since '56, so reason to change.

2. ADD a relay such as an SR501
The wall wart solution is the easiest
Any benefit to the relay? (bit more complicated wiring, but I am a EE, so I'm sure I could handle it )

There's an outlet right on the back of the boiler, so that's easy enough - what would be the correct wiring from the transformer to the aquastat/thermostat?

Is your hot water from the taps REALLY REALLY HOT?
Do you know if there's a 'thermostatic mixing valve' on the hot water piping coming off the boiler and going to the home?
It's can be hot - would be 160-180 based on the aquastat, right? No, no one young enough or old enough (or dumb enough!) to not realize - appreciate the concern though! (Wife likes the hot shower - not sure how she stands it).

There is a manual valve that connects the cold to the hot after the boiler that is closed... but that's seems to be it...

So I'm sure I can get the transformer connected, with a wiring diagram...

Bigger question of course, based upon the boiler/burner, do you think I should look in to replacing with a new unit with separate hot water heater? Always hate hearing the burner kick on when it's 95 deg outside...
 
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Old 11-21-14, 07:49 PM
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what would be the correct wiring from the transformer to the aquastat/thermostat?
That's the part that's gonna be tricky, how to determine, without taking the aquastat apart to reverse engineer, which one of the T terminals is connected to the transformer, and which is connected to the relay coil...

Let me sleep on it.

There actually IS one more option, but it involves taking the board out of the aquastat and soldering a wire and bringing it out for access to the "C" connection.

If you are an EE, perhaps that's doable.
 
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Old 11-21-14, 11:20 PM
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So, looking in to the wiring some more... the wiring runs out the bottom right and connect to a 4x4 box at the back of the boiler... from there, we get incoming 120V, wiring to circ and wiring to burner. It's a mess of old wiring, but I'm figuring the reason that C2/B2 are not connected on the aquastat, is that they are just nutted together in the box (C2/B2 are just the 120V common, right?). As you said, the L1 (hot) is jumped to ZC, bypassing the low-limit/circ control for the circ... still no sure why would one do that?

Saw another post somewhere that said the "C" wire should be taken off the load side of the transformer, on the schematic - right to the right of the 1K resistor - that seems right, as that's the 24VAC common side of the transformer... then Rh should be the "hot" T terminal, and W the common T terminal (to the left of the 1K)... that sound right?

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Old 11-22-14, 06:04 AM
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still no sure why would one do that?
No, me either, but we'll never know. Chalk it up to one of those mysteries of life.

right to the right of the 1K resistor
Drawn as a resistor, but that's actually the relay coil. I don't know why they don't follow standard schematic symbols.

then Rh should be the "hot" T terminal, and W the common T terminal (to the left of the 1K)... that sound right?
Yes, that is correct.

If you do pull the board to add that wire, be careful with the small capillary tube that the sensing bulb is on. Don't kink it or you'll be buying a new aquastat. When you reinstall, make sure the sensing bulb goes all the way to the bottom of the well and stays there.
 
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Old 11-22-14, 06:17 AM
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Drawn as a resistor, but that's actually the relay coil.
Yes, I'm reading the symbols, but I understand it's the relay...

It would seem that by jumping ZC to hot, the circ would always run when there is a call for heat... I read this on another site (Aquastats: Setting & Wiring Heating System Boiler Aquastat Controls, how to set the HI limit LO limit and DIFFerential dials on controls like the Honeywell R8182D Combination Control Aquastat) - maybe that explains why they did it:

"In Canada boilers operate a bit differently: the circulator pump may be set to run continuously, and the thermostat just turns the burner on and off. This gives more even heat and helps avoid a frozen heating zone pipe in very cold climates."

I'm not in Canada (on LI in NY), but maybe some tech thought it would heat more evenly and the boiler was big enough to run circ AND provide DHW...

OK, I'm going to get some tools and we'll see what happens...
 
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Old 11-22-14, 07:27 AM
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Inspectapedia has grown into a pretty useful site over the years. I can't recall finding any terribly erroneous information there.

I scanned the link you sent, and a few of the bread crumb trails to other articles and noted that they mentioned removing and capping the BLUE wire to disable the LOW limit control. While this will disable the BURNER from firing on LOW limit, it will NOT disable the 'lockout' of the circulator.

The way I always propose to COMPLETELY eliminate the LOW limit burner AND circulator lockout is:



Not that you would want to do this since you are still using the boiler for DHW, but for information only.

It would seem that by jumping ZC to hot, the circ would always run when there is a call for heat
That's correct.

I'm going to get some tools and we'll see what happens...
So that future techs don't have to puzzle over that extra wire, document the change in some way and keep with boiler. Mark the wire as " C " in some way. Also, for future reference, label the T T terminals as " R " at the terminal connected to the transformer, and " W " at the terminal to the relay coil. (I think you are planning to do this anyway, this is a reminder for future readers...)
 
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Old 11-22-14, 08:29 AM
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OK, PCB out of aquastat and take a look at this... figured I'd post pic, while I try to figure it out...

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Old 11-22-14, 09:03 AM
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Oh boy... to coin a term, " WTF were they thinking? "

Let us know, if you can, by marking up a schematic, what exactly they've cut and jumped.

I bet it was completely unnecessary. They could have probably done the same by pulling a couple wires and using a wire nut.

I bet that's the burner circuit...
 
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Old 11-22-14, 09:23 AM
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The two scratched out PCB solder points to the right and left of the white wire, isolate the 'hot' side of the transformer and the white wire was relocated there from the point next to the YL wire... the black jumper wire keeps the connection from the hot L1, through a jumper on the front S1 to S2, down to the RD (now bypassing the 'hot' side of the transformer)...

BUT... I labeled New "C" as the common 24VAC side of the transformer, so that is where I should add a wire for the thermostat... simple enough...

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Old 11-22-14, 10:08 AM
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I bet that's the burner circuit...
No, it's not.

I know what they did, but I don't know why they did it.

They cut the copper and isolated the hot side of the transformer primary.

Then they rerouted that white wire to the primary hot from where it was at the ZC terminal.

At least I think that's what they did...

Can you post a shot of the top of the board with the other wires out of the way?

OOPS! you posted before me... I just did the same thing! I'll post my pics in a couple minutes after I study yours to see if we agree. I think we do, great Engineers think alike!
 
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Old 11-22-14, 10:53 AM
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This is just weird... why would they do this?

The way this is modified, when the boiler cools to fire at LOW setpoint, R-W BREAKS and power is removed from T1, thereby preventing K1 from operating and circ from running. At the same time R-B MAKES and the burner will fire to bring boiler back up to temp, at which point R-W MAKES and power is restored to T1 and K1 can operate. At this time R-B BREAKS and burner shuts down.

What's the point? I don't get it!

The end result is EXACTLY the SAME as 'pre' modification! With the exception below:

You are actually going to have to reverse that modification because if you don't, whenever the boiler fires on Low Limit, your thermostat will lose power.
 
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Old 11-22-14, 11:09 AM
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Did this and put all back together - although I was pretty sure that since the hot side of the transformer is isolated, it won't have constant power, so the new "C" won't always be lit up - and then this:

You are actually going to have to reverse that modification because if you don't, whenever the boiler fires on Low Limit, your thermostat will lose power.
which has now been proven true...

So I think I'm back to square one with the "C", as there is no place to get a constant 24VAC with the modifications that were done...

Why was this done? Options? Maybe I should just get this Honeywell L7224U Universal Oil Heating Boiler Electronic Aquastat Controller and be done...

Or, I just undo what was done - then my "C" should work... really wish I knew WHY they did it...
 
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Old 11-22-14, 11:17 AM
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really wish I knew WHY they did it...
Yeah, whoever did it probably wishes they did too.

I would definitely undo what was done, you know how...
 
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Old 01-26-16, 10:41 AM
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Hi! I got same aquastat and also wanted to add smart Thermostat. I tried to follow all that you saying but I'm not sure I understood why couldn't Common wire be added to that transformer solder joint? Is it because there's no constant +24V on R or W wires?
Is there anything else that can be done?
Did you eventually replaced it with L7224U?
 
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Old 01-26-16, 11:40 AM
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You've read the thread. Are you handy enough to take the control box apart as you need to solder a wire to the back of it ?

With TT terminals one is R and one is W. They are labeled clearly in post 21. The wire you add will be the needed C connection to run the stat.
 
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Old 01-26-16, 01:09 PM
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I would just get a wall plug transformer. Run wire down from t stat in wall to floor level. Poke hole after removing molding and pull wire out... Run wire along floor to nearest outlet. Then replace molding to hide wire...

Robot Check

Kind of like this.. There is a better site that shows this but I cant find it...

https://www.youtube.com/watch?v=8a_f2_iAW1U
 
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Old 01-28-16, 06:58 AM
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Yeah I'm pretty handy with my soldering station (soldered PCBs with over 600+ SMD components by hand) Up to post 21 it seems good and logical, and then in post 22
So I think I'm back to square one with the "C", as there is no place to get a constant 24VAC with the modifications that were done...
Which confused the hell out of me
Lawrosa, that's a great suggestion! I was wondering why all those smart thermostat don't just include option for external power... I thought it might interfere with existing aquastat or something Watching video right now.
From what I understand Positive 24V from external transformer is connected to R wire?
I'm thinking instead of making those extra holes, I can install transformer near furnace in the basement and run 2 wires up the "chimney hole", that's where all the wires are now (thermostat was actually placed on the wall behind chimney so wiring goes straight up without any obstructions)... It's 2 floors straight up. 18 AWG wire should be ok?
 
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Old 01-28-16, 08:30 AM
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The C wire can be obtained. The problem with that poster is that if you read the whole thread.... his control box was additionally modified.

You can mount a second transformer anywhere and bring the power to the stat. #18 thermostat wiring is the norm for wiring.

If you use this method..... the existing two wires connect to Rh and W.
The new transformer wires connect to Rc and C.
There should be no jumper between Rh and Rc.
 
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Old 01-28-16, 11:24 AM
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Thank you so much! In that case I don't want to touch Aquastat at all. I recently moved to this house and most of the times I "touch something", I discover problems
Ordered transformer, wire and Ecobee3 If anyone is interested I'll report back how it worked, once I hook everything up!
 
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Old 01-31-16, 03:59 PM
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It worked! Transformer I got from Amazon was DOA, but I was able to hook up new wiring to existing 24V transformer (one that's connected to valves).
 
  #31  
Old 10-21-16, 07:59 AM
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Wall wart

Any recommendations on the 24v wall wart?

Also, how many amps should it be supplying?
 

Last edited by mringer14; 10-21-16 at 08:44 AM. Reason: Adding info
  #32  
Old 10-22-16, 07:23 AM
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Use an 40 VA or .3 amp transformer designed for residential heating/AC service. See:

Transformers , Honeywell Transformer , Honeywell Control , Transformer - SupplyHouse.com

Typical consumer grade wall warts, may not meet code standards and are not something to rely on during cold winter days.

Be careful on systems with both heating and air conditioning where each has its own 24 VAC source. Modern thermostats have separate terminals RH (heat) and RC (cool) for when there are difference 24 volt sources. Other side of both 24 volt sources go to "C"
 

Last edited by doughess; 10-22-16 at 09:56 AM.
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