Carrier BW9 Burning Up Transformers

ShawnC715

I am in the process up updating my radiant heat system.  The system was set up with four zones, but only had one thermostat and all circulation pumps ran 24-7 simultaneously. The thermostat just fired boiler.  I added a Taco SR 504-4 and Ecobee 3 lite Thermostats. I am powering the thermostats from the 24v transformer onboard the Taco SR.  The SR and the thermostats work as they should. When there is call for heat the pumps starts up.  I ran into an issue when hooking the boiler up to the SR end switch. My understanding  is that the end switch just connects the two wire when energized. So I figured I could connect the wires that went to the old manual thermostat from the boiler to the end switch. In doing so I made a major error and let the 24v wire from the boiler contact ground while it was hot and it burnt up the transformer. I put a new one in with the same specs and it lasted five minutes or so and burnt up. Then I set it back to the original configuration using the original thermostat and it fried the transformer again. I have fully inspected all wire and the control board. I don.t see anything burnt up or contacting ground. I have already contacted the pros, but they probably won't be able to get them out here till next week.  Hoping some one has an idea of something I can test. The 24v does not seem to have alot on it so I am not sure what to check

109A_5

Hello @ShawnC715,

What do you need the second transformer for ? Just wire the Taco SR 504-4 up per the manual.

I am a bit confused, is the transformer that powers the Taco SR 504-4 burning up or a second additional transformer connected to some random place. If the transformer that powers the Taco SR 504-4 is the one that is burning up you may have damaged the Taco SR 504-4 unit.

Edit: Is the transformer in the boiler burning up ?

You could connect the old manual thermostat in parallel with the boiler TT or the Taco SR 504-4 XX but with the Taco SR 504-4 now controlling the circulators it seems almost pointless.

ShawnC715

My apologies, yes the transformer on the boiler.  The transformer on the boiler provides 24v  power to the control board on the boiler.  So, when it burns up the boiler will not do anything.  My intention was to  use the switching relay to run all the zones and that end switch "XX" would would turn the boiler on when there was a call to heat,. It actually did work for a minute or so when I had the replacement transformer installed. I only hooked the old thermostat back up to isolate the boiler from the switching relay to determine if it was a boiler issue or if it was burning up because of the way it was wired to the SR 504. It burned up the 3rd one hooked up in the original fashion. I have another structure on the property with the Dunkirk version of this boiler and was able to swap the control board , so I know that is not the issue, but without seeing something obvious I have no clue what it could be.

109A_5

Hello @ShawnC715,
OK got a better picture of the situation. Sound like you have eliminated these things as being the problem.
1) the old thermostat
2) SR 504 (XX should be isolated anyway)
3) Control Board
Looking at the Ladder wiring diagram there is not much else there. I hope you have a multi-meter and know how to use the Ohms function.

I'm going to guess first;
Assuming terminal 5 of the secondary of the transformer is grounded by the gas valve or the Control Board.
Due to the over-current event the wire (Red annotation) from the transformer (terminal 4) to and through the "Casting Temperature Sensing Safety Switch" (Orange annotation) on its way to the R terminal has melted the insulation and the wire is touching ground somewhere now.

Or the "Casting Temperature Sensing Safety Switch" (Orange annotation) had a meltdown and is now shorted to ground.

A troubleshooting method; With the boiler wiring all intact, disconnect the transformer at P2 what is the resistance looking into P2 towards the board. If near zero Ohms disconnect P3 and see what happens. If not near zero Ohms look at "Casting Temperature Sensing Safety Switch". That hot side of the 24 VAC appears to get to the thermostat R terminal (on the boiler) looping through the Control Board. So the short could be on the transformer side wiring or the side leaving the Control Board and going to the thermostat R terminal (on the boiler).

Additionally with P2 removed from the Control Board, with the Ohmmeter looking towards the transformer and the "Casting Temperature Sensing Safety Switch" (Orange annotation) either P2 terminal to ground should read infinite (no short to ground).

ShawnC715

Thanks so much for you time assisting me. I checked the wires that go to that casing safety switch and did not find any irregularities. I checked the switch itself and it is closed, zero ohms of resistance across the pins and no short to grounds. I also checked the purple wires that run to the differential pressures switch and the brown wires running to the high limit aquastat. Again no irregularities and no shorts to ground. In addition, I checked the wires to the gas valve and the wires themselves checked fine. I checked the outside pins of the on the gas valve and the had 40 Kilo ohms of resistance (I believe). I know this check is difficult since it goes to the circuit board of the valve and goes to a rectifier. I am wondering if i didn't burn up the circuit board in the gas valves, it is really the only thing I have not triple checked. I was worried about taking it apart because I have read a few thing that say if you take them apart they are garbage and need to be replaced. My next step is to get a few inline 2amp fuses and put them on both secondary leads with everything disconnected and plug in the least like to the most likely circuits in succession until I find the issue. I was able to get 5amp circuit breaker locally, but even with that in place it burned the transformer up. I will have to wait on my Amazon order, but hopefully the 2 amp blade fuses will pop before it burns up a 4th transformer. I also have a call out to the local HVAC Tech , but seems most want to sell you a Combi-Boiler instead of fixing what you have. If you think I am missing anything, please let me know. Again thanks for being so generous with your time.

109A_5

Hello @ShawnC715,
A few things;
I went for the current carrying conductors that should have had the over-current event's current. Was the boiler's R terminal shorted to ground or something else ?

Does it only burn up the transformers when there is a call for heat ?
Compare Ohmmeter readings of the gas valve to the other unit you borrowed the control board from.
Edit: From what you described I don't know why that would hurt the gas valve.

Instead of popping a lot of fuses, use an incandescent lamp for a current limiter, inserted at terminal 4 of the transformer or the transformer side of the "Casting Temperature Sensing Safety Switch" if you are confident that wire is good.
Use two 1156 automotive lamps in series for 24 Volts at 2.1 Amps. The lamps will be bright with a short and a lot dimmer when the short is removed. No wasted blown fuses, visual indication, self resetting, with different lamps and/or series - parallel quantities the Voltage and Current is programmable for other applications.

And you won't burn up the transformer during troubleshooting since the lamp(s) limit the current indefinitely.

If you want a bit more current, like about 2.75 Amp limiter, use a 1157 lamp and connect the major and minor filaments in parallel and then in series with another 1157 lamp with its filaments paralleled.

ShawnC715

I will try the lamp technique.   To answer your question,  I am no exactly sure which side contacted ground since both wire for the thermostat wiring are yellow.  One contacted the body of boiler and burned up up the transformer. It seems to be when there is a call for heat. The third time it burned up it was very fast but it was hooked to the original thermostat so I assume there was an instant call for heat. Does it matter which leg is connected to Rh and which one is connected to W ? Given that both wires are yellow, I did not pay attention when I reconnected the original thermostat. I will check the other gas valve resistance and see if the results are similar.

109A_5

Hello @ShawnC715,
Hope you caught all of my edits of the previous post.
Assuming this happened (R terminal shorted) and the green annotation is the grounded side of the secondary of the transformer. Grounded side P2-2 could be verified with an Ohmmeter with P2 disconnected.

109A_5

Hello @ShawnC715,

If you flip it around, say if the R wire is actually grounded and you shorted the W wire to ground the only thing that should have happened is the boiler would have fired up. R wire being grounded would be odd.

109A_5

Hello @ShawnC715,
If in fact the overload only exists when the R and W are connected (call for heat) I would check all the limits along the Blue annotation. Fairly easy to do with an Ohmmeter or disconnect them (one at a time) in a logical order while viewing the test lamp(s). Maybe something else was disturbed or melted causing the present overload.

EdTheHeaterMan

Had to put this one out there for everyone to sing along

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The wi-ring was askew 🎵
🎵 I of course replied
when a transformer dies
smoke gets in your eyes. 🎵

Get the all new Fast acting Non-patented
SMOKE KEEPER

Disclamer: I do not really sell that device. You can get the necessary components at your local auto parts store.

ShawnC715

Thanks for your thorough answers and suggestions. Fortunately our temps are staying above freezing for the most part and my window heat pump is keeping up in the main area of the house. I do not have a lot of options around here for setting up the incandescent lights. So it looks like I will have everything that I need by Wednesday to proceed.

I checked the Dunkirk Version that is in the other house and it actually uses a different gas valve. I did check the pins on that one and it is showing O.L. I rechecked the other one through the wires, coming from the board plug and the reading was 12 Milliohms. I also did a search and found DIY blog where a guy was having similar issues with a boiler and it turned out to be the gas valve. I have checked those series of safety switches annotated by the blue and they all seem to be correct. All the switches are closed with zero ohms of resistance no shorts to ground in the in the switches or the wiring. I was able to find an "open box" replacement gas valve for $30 on Ebay. So I will have it, if I need it. If not, I am only out $30. I will let you know what I come up with once, I get everything and get it tested.

109A_5

Hello @ShawnC715,
"12 Milliohms" so actually 0.012 Ohms, not good. Auto-ranging Ohmmeter ? I would disconnect the wires at the Gas valve and test the Gas valve directly.

With your account of what started this whole thing I don't see how you could have damage the Gas valve, it runs on 24 VAC.

The 1156, 1157 Lamps are available at any auto supply store, many auto supply store also have the sockets too with wire pigtails or I have acquired the lamp sockets from a junk yard when I was there for another reason. Way back when the lamp bases were brass I just soldered the wires directly to the lamp.

ShawnC715

I actually have no clue which pins to check on the gas valve.  There are five female pins on the plug and four male pins on the valve itself. I figured I would just disconnect the plug from the board and determine which where the live pins by doing an ohms test. This is where things got confusing. If I put my leads on the two wires as the come out of the board they are open, not somehow fused together and not grounded out. When I checked which pins each wire goes to I found that the both go to the far right pin with 4+ milliohms of resistance each. It turns out this plug has a rectifier built into it so I am at a loss of what I I should check other than doing the light check that you suggested. I am working all week so, I will just wait for my Amazon order to be delivered and work on it in the evenings. I took a picture of the plug, maybe you have experience with these. It doesn't look like there are any replacements available if this is the issue.

109A_5

Hello @ShawnC715,
I hope you are not confusing Meg-Ohms with Milli-Ohms. Most common DMM (Digital Multi-Meters) don't have resolution down to the 4 Milli-Ohm area 0.004 Ohms, but they easily go to 12 Meg-Ohms or 12,000,000 Ohms which is almost infinite or an open circuit (as far as the meter is concerned). Auto-ranging often does not help either.

That gas valve probably has a DC coil or as they call it RAC (Rectified AC). I think they use it because in situations where they want to throttle the gas valve it works better than a gas valve with an AC coil.

With the gas valve disconnected from the control board at P3 your Ohmmeter measuring P3-2 to P3-5 toward the bridge rectifier (which may be inside the gas valve cable connector) I would expect it to read Open, OL or in the Meg-Ohm range since DMMs typically in the Ohms mode won't apply enough voltage to forward bias two diodes. And even if it did the resulting reading is not accurate due to the voltage drop across the two diodes.

The Diode check mode (the Diode symbol on the meter) if you meter has it may help but it really won't tell you if the gas valve coil is shorted. With the gas valve disconnected from the control board at P3 your meter measuring P3-2 to P3-5 toward the bridge rectifier I would expect a reading in the 1.2 to 1.6 Volt range, probes in either direction, if there is just a bridge rectifier hidden in that molded connector.

If the bridge rectifier is in the molded connector the Diode check mode may help you analyze the cable connections. Each diode will be 0.6 to 0.7 Volts in the forward direction only.

My decades old AC gas valve coil measures 44 Ohms, I would expect yours should be in the same ballpark if you find the correct pins to measure under that molded connector at the gas valve and if the bridge rectifier is actually in the molded connector.

ShawnC715

Yea, I am sure you are right. It is an auto ranging meter and I saw the "M" in the corner. So, yes I was confusing the Milliohms and Megaohms. I use that function as a continuity tester essentially and then use the voltage function, other than that I am limited with my electrical knowledge. I do have automotive tester that has the diode function. I have used it in the past to test voltage regulators on UTV's. It seems like best option is to just wait and do the elimination test with the incandescent lamps and see what I find. I am going to start with everything disconnected in the 24 volt circuit. Then i will add the thermostat and make sure there is a call for heat. Next, I will plug in the board, then all the safety switch one by one. After that I will plug in the gas valve. Hopefully, that is good logical progression.

109A_5

Hello @ShawnC715,
For some added clarity; With the battery powered DMM (Digital Multi-Meters), at least the ones I have used, the open circuit Voltage across the probes in the Ohms mode is usually less than 0.6 Volts. This gives readings that are more purely resistive when poking into complicated circuits since the low voltage can't forward bias diodes and/or transistor junctions.

With Diode check mode the open circuit Voltage across the probes can be up to about 3 Volts and the display readout is in Volts DC. So you can see the forward voltage drop across a Diode.

With Continuity test mode and the 'Beep' annunciation. The open circuit Voltage across the probes may vary depending on the manufacture of the meter. And I've seen meters 'Beep' at almost 100 Ohms so I usually don't use that feature much. To me 100 Ohms may be continuity but a good normal wire should be less than 1 Ohm and a 100 Ohm wire would be bad.

"I am going to start with everything disconnected in the 24 volt circuit. "
This method will work. Although I would have the Boiler powered down when connecting or disconnecting P3, since there is so many different circuits going through P3.

Additionally, I like to see the fault, bright lamps, and then work toward dim lamps by eliminating circuit paths and devices. That way if I bump something (crushed or melted wire insulation, etc.) I can see the problem go away 'instantly'. The other way you could inadvertently clear the fault and not know it or where it was.

With Lamps in series with the circuit (often used instead of the fuse that keeps blowing) works so amazingly well and is the oldest technique in the book, I'm surprised it is so seldomly used. It works where expensive meters just leave you lost.

The Lamp(s') overall Voltage just needs to match the circuit Voltage and the Current limit value can be calculated using the Wattage of the Lamps if the Lamp's current is not known. The Lamp's Current should not be more than the fuse value. You just need the correct Lamp(s) for the circuit under test (12, 24, 120, 240, etc.).

ShawnC715

I just wanted to give you an update. I set up the test lamp that is pictured in the diagram above. Once I connected everything, the lights did not illuminate at all. I did hook everything up with the exception of the gas valve and the system did everything except fire. It went through the three cycles of trying to start with not issues. I already pulled the gas valve and the new one arrives today. I plan on installing it once it arrives and try again with the test lamps in place. Is it common for the lamp to not illuminate? I assume they are still doing their job since it powered up.

Jamie Hall

If the gas valve is not present, as I read that circuit diagram there is no path to ground -- and the lamps won't light. No surprise there. I doubt very much that you have proved anything at this point... and I hear the distant rumble of the parts cannon being fired at random...

109A_5

Hello @ShawnC715,

I don't know if the wiring diagram and ladder diagram are totally complete. If they are the control board may be predominantly or totally be power by 120 VAC. The gas valve may be the only true normal load on that transformer that is burning up.

With no load or a very minimal load the lamp(s) will be dim or no light visible, that is normal. With a Short circuit they will light up brightly. Without the lamp(s) you would be burning up another transformer or blowing fuses. When the lamp(s) are in series with a normal load, how bright they get really depends on the normal load and the lamp(s) used. In this case, with a gas valve that is normal they may be half bright and the gas valve may open or it may not.

If the gas valve only draws 0.7 Amps (see picture) I would expect the Lamp(s) the be on the dim side with normal operation since the lamps are rated at about 2.1 Amps.

A guess from here is the rectifier in the gas valve (or connector) was damaged or the gas valve coil is shorted. Since it seems you are not finding anything else.

With what you were doing when this all started, I not sure what would cause that type of damage. Maybe something happened that you were not aware of. Could 120 VAC have been applied to the gas valve circuit ?

If all is normal and the control board goes through its normal cycle with the gas valve disconnected you should see 24 VAC at the connector P3-2 to P3-5 (that normally goes to the gas valve) when there is a call for gas.



With the lamp(s) connected up at one side of the transformer and all the other connectors connected I would see what the system does, and at what stage the defect comes into play.

ShawnC715

I received the gas valve yesterday and installed it. Still no lamps illuminated and everything worked as it should. Initially, I had it hooked up to the original thermostat. Once I saw that it was working fine, I hooked it up to "XX" on the switching relay. I never really paid attention to weather the power light on the Taco SR 504 4 came on initially, but I did not hear anything happening and noticed that none of the lights were on. I did not confirm this, but I assume I burned up the transformer on the Taco somehow. I ended up switching back to the original single thermostat and and wiring all pumps together on their own dedicated circuit. The system has worked for years this way. It is not ideal, but it is getting cold here, so I can't risk messing with it and being without heat again. I have a transformer with a circuit breaker that I will replace the Taco transformer with so two of the pumps will come on only when there is a call for heat. I could run the third zone, which is the main living area off the boiler pump wires. I am not sure if this might be an issue or not, but I am using Ecobee Lite 3 thermostats and have the "C" blue wires running the 24v post on the Taco 504 4. Or is it possible there is still an issue with the boiler wiring but the with the two incandescent lamps in place it has the flexibility to continue to work. The gas valve did not come with a new plug, so their might be an issue with that rectifier plug, but I did see anywhere to get one of those. I did test it at did see 24vdc on the outside pins momentarily while it was going through its firing sequence, but it is difficult to get a good reading on it without the constant power going to it which you only get when it is running.

109A_5 thank for all the time and information you have given me. I think the incandescent lamp trick is what has this thing going. I am just going to leave them in place since it working and I have heat. I am in the middle of pulling radiators for sandblasting and powder coating. I have five more to do next summer, so I will try to get to the bottom of what is going on at that time.

109A_5

Hello @ShawnC715,
OK, do what ever you need to do and stay warm. The Taco SR 504-4 is not a new product and there is probably thousands of them out there doing what you are trying to do with it. It helps neaten up the wiring and provides indication which is good for verification and system troubleshooting. And another 24 VAC power source for system equipment.

If the system works correctly you can leave the Lamp(s) in circuit (if desired) as long as the system works correctly and if a short does happen to occur their heat does not damage anything nearby. They would be like an indicating self-resetting fuse. But they are not a fuse and they do not break the circuit like a typical fuse does when a fault happens, they just limit the current to a safe amount. So transformers don't over heat and fail. An actual (maybe 2 to 3 Amp) fuse is a good idea if the lamps are ever removed, they are probably cheaper than transformers.

By the way an incandescent lamp's cold resistance is much lower than its hot resistance which it why they work very well in troubleshooting situations.

Possibly where things took a bad turn with your situation is all power (to all the equipment ) should have been de-energized during the re-wiring of the system. Once the re-wiring was compete and the wiring was double checked for correctness then re-energize the equipment and test for proper operation.

hot_rod

The Caleffi 5 and 6 zone valve relay boxes come with two 40Va transformers installer. They snap in and are easily replaced with any foot mount type. Circuit breaker protected so no fuses or light bulbs needed if you short something.

This can be easier than trying to phase separate transformers together when you have high load zone valves.

The transformers are in parallel, so you have 80Va available across all the valve connections.

109A_5

hot_rod said:

The Caleffi 5 and 6 zone valve relay boxes come with two 40Va transformers installer. They snap in and are easily replaced with any foot mount type. Circuit breaker protected so no fuses or light bulbs needed if you short something.

In this case the transformer that was failing was in the heating equipment. I don't think the transformer(s) in the zone valve relay box would help any and were not failing. Their purpose it to power other control equipment.

The light bulbs are intended as a troubleshooting aid, so much better than burning out transformers and countless fuses and/or continually having to reset circuit breakers like the 'Little Popper' until you find the defect.

In general folks can troubleshoot the hard way or not, it is their choice.

ShawnC715

I was able to find a rectifier plug and ordered it. $30 is worth the piece of mind knowing that it is good and my boiler won't fail on a below zero day. It is really the only thing I have not been able to rule out. I asked local HVAC tech about swapping the valve out to a non-rectifier unit and he said they could not do it due to liability. It seems like that is a more straight forward set up. This unit is 18 years old and I hope to get a lot more years out of it. I just don't trust any of the new units they are installing for any sort of longevity.

109A_5

Hello @ShawnC715,
It seems to me replacing the gas valve repaired the issue. So with the original gas valve the coil is either shorted or possibly one side of the coil is shorted to the housing (ground).

Two things that bother me in this situation, that has not been proven.
1) The original gas valve's integrity. (Example; new coil is 60 Ohms, old coil is 2 Ohms)
2) What caused the gas valve failure (once proven). Why would it fail when it did ???

Connecting the XX terminals of the Taco SR 504-4 to the boilers R and W should not have caused a gas valve failure and it would appear that there was a limit switch open anyways (if the boiler was not active).

So to me if you don't know what cause the failure, it could happen again.



Anyways spare parts are good.

ShawnC715

I am not sure entirely. The problem started initially, when one of the thermostat leads from theboiler came into contact with ground while it was still powered. After replacing the transformer and connecting to the Taco SR, it burned up another transformer when there was a call for heat. The 3rd transformer went with the original thermostat and a call for heat. I did find out what caused the Taco transformer to go, well I narrowed it down to one of two things or possibly both. One of the thermostat wires may have been compromised by a wire holding staple and /or the W and the C wire might have been switched on the thermostat. After replacing the transformer in the TACO, I noticed some irregularities with one of the thermostat wires and replaced it. I also noticed that the 24vac wire lugs on the TACO SR are not the same. The bottom one will supply 24vac and the top one is the same as the "W" connection. Originally I might have had that C wire from the problem thermostat in that top post. so if I had the wires swapped at the thermostat, it would make sense why the thermostat originally worked. Then I pulled the wires and when I hooked it back up, I had both C wires going to the bottom lug, which caused the TACO transformer to go. Well that is my theory anyway or one of the staples damaged the wires and caused them to come in contact with each other. It is working perfectly now, and should save me money on propane and electricity, not having those three pumps running 24-7 for the entire heating season. I am also confident that I have learned quite a bit that will help me with the other house I have to retrofit over the summer. Thanks again for all your time and information.

109A_5

Hello @ShawnC715,
Maybe I missed it along the way, but I did not realize the transformer in the TACO burned up also. I just thought you had two transformers in the boiler burn up.
The thing that bothers me is why did the 2nd boiler transformer burn up and in all the chaos how did the gas valve get damaged ?

Anyway, OK, good that you are up and running.