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Taco Switching Relay Fried Twice--Tstats at fault??

I had a Taco SR504-4 switching relay that's only 3.5 yrs old. Never had an issue but over the weekend I noticed my ecobee Tstat screen was blank. Went down to check boiler and it was on, but the board was lifeless, no lights or anything.

Thought it was a fuse so checked all those and nothing. No heat now so called HVAC and they indicated the board was fried. Boiler on same circuit and fine, no power loss, no breaker tried on that circuit.

They come out today to put a whole new board on and they had a theory that the ecobee Tstat may be the culprit. Don't see how but after the replaced the board they put on my old battery operated Tstat temporarily until I got my new ecobee. Call ecobee and they say no way could the Tstat be the issue and have me swap it with my other ecobee in other room. It fires up right away and he says it's fine. Put it back where it started and remove the old battery operated Tstat and shortly after another POP! on the board, and it's shot.

HVAC comes back out and replaces the 24vac transformer to get me running again and needs to come back to replace the whole board again. The supposed culprit Tstat is now in my other room running to an air handler for my kitchen no problems.

HVAC says ECOBEE is the problem, ECOBEE says no way it's the problem. Guy left scratching his head and I'm pissed b/c I just paid them a lot of money for the call and there seems to be no answer to what's going on....

THOUGHTS PLEASE!!!
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Comments

  • ScottSecor
    ScottSecor Member Posts: 843
    Not sure if I missed it, but I'm not sure if your controling zone valves or circulators. If zone valves is there any chance they are drawing more power than the transformer ratings? If circulator pumps is there any chance the pumps draw more than the relay is rated for?

    We've installed more than a hundred Taco relays over the years and have had very few problems (zv and pump types). We do not install ecobee stats nor are we fans of them. Any chance it's not the panels fault or the thermostats fault and instead a short? Any chance someone hung a picture and accidentally shorted out ther transformer on the panel?
  • jac34
    jac34 Member Posts: 63
    All good points....we are using 4 taco circulators. I believe he checked those so I think they were good.

    It's been running for a few hours with the new 24v transformer with the supposed culprit ecobee in another room powered by an air handler. All working fine so far, but a short is what I was thinking too. Maybe a mouse chewing on a wire?? If so, wouldn't the breaker pop on that circuit before the board blows out?

    They are coming back tomorrow to do more investigative work but hard to think a smart Tstat could be the culprit.
  • ScottSecor
    ScottSecor Member Posts: 843
    In simple terms, if you removed a thermostat from the wall and twisted the wires together, the heat would work fine, it just would not shut off. This would not cause issues with the relay or the "internal" transformer. However, if somehow you grounded the thermostat wires you could wreak havoc on the relay and or the transformer. So in the real world, if one of the thermostat wires (copper conductors, not the insulating jacket) is somehow rubbing on a metal object (copper pipe, steel pipe, perhaps ductwork I guess) it might be shorting out and causing your headaches. Another way to put it, if you did what I described in the first sentence, and somehow touched these wires to a copper pipe it would likely cause the fuse to break or possibly blow the panel/transformer.

  • Jamie Hall
    Jamie Hall Member Posts: 22,941
    Do you have one transformer or two? And is the thermostat powered with a C wire? I'm very much inclined to think it is neither the Ecobee nor the board itself -- but something in the wiring which is ending the board too much voltage under certain conditions.

    This may be difficult to track down, however I would closely examine the wiring and I would test it -- disconnected at both ends -- with a multimeter. Assuming we're looking at three wires here, none of the the three should show a short to ground, but at least as important is that none of the three should show a short or even anything less than a megohm resistance from one to another, in any of the three combinations. Assuming they pass, hook them back up to the board and transformer exactly as they were before, but don't hook them to a thermostat. Now between the two connected to the board -- nominally "r" and "w" -- there may be a voltage, but that is not all that important. However between the one labelled common, going to the transformer, and "r" there should be 24 volts, approximately. If that's still OK, try just twisting r and w together; the zone should turn on. Again measure the voltage between r and common -- it should still be 24 volts.

    Can't go farther than that at the moment -- there are other checks I'd make if I were there, depending on what I found above.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    kcopp
  • jac34
    jac34 Member Posts: 63
    I have one transformer inside the relay board, which blew twice on 2 different boards. All Tstats are powered with a C wire, but only one of them is powered from this relay board, the other 2 are powered by the a/c units which is why they did not go out when this board blew.

    The Tstat wire that seems to be the issue is traceable except for a 2 ft length going up the wall. Everything else looks good.

    I will see what they come up with tomorrow and try your suggestions above.

    Thanks!
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,344
    Adding you own relays and larger transformer & a fuse will prevent this blowing up of boards
    mattmia2
  • mattmia2
    mattmia2 Member Posts: 9,467
    are any of the t-stats connected to both heating and cooling?
    wmgeorge
  • HomerJSmith
    HomerJSmith Member Posts: 2,403
    edited February 2022
    Ok, a class2 transformer has a fuse wire in the primary of the transformer. If there is an over current event the fuse wire melts, cutting off the 110 v to the transformer.

    Does the cover to the Taco have a plastic or metal cover? Does it have fuses for each relay or one single fuse? The maximum current draw for all the relays + pumps + thermostats is, I believe is 20 amps. Exceeding 20 amps should blow a fuse. A picture of the exposed relay board would be helpful.


    The only thing that would blow the fuse wire in the transformer would be a direct short of the secondarys. If you have one fuse that fuse is to protect the transformer from an over current event. What is the rating of that fuse? Did that fuse blow or just the transformer? What do you mean when you say the Taco got fried?

    How is the Ecobee wired up? You have a red and white wire at the thermostat? Is there also a green wire? Is it 2 conductors or 3 conductors? How is the Ecobee getting its charging? What do you mean when you say it has a C wire and how is it connected to the Taco and the Ecobee? Are you using the Ecobee charging adapter? Pics of it all, please.

    Look, the Taco has a 110 Vac power supply. It is either hard wired in to the Taco or it has a line cord that plugs into a wall outlet. I would check the polarity of the AC going into the Taco box.

    I eagerly a wait your answers.

    PS. It could very well be the Ecobee if there is an internal short between the Rh and the C connections or the thermostat wire connecting everything.
  • SteveSan
    SteveSan Member Posts: 231
    Have you've tried to disconnect all the t-stat wires going to the sr control and jump the r-w for each zone? If the red LED lights comes on and everything works as it should then you know it might be a t-stat issue. From there I would connect 1 of your t-stats at a time to see what happens.
  • Zman
    Zman Member Posts: 7,549
    If one t-stat is controlling two systems, my guess is that is the issue.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    mattmia2SuperTech
  • jac34
    jac34 Member Posts: 63
    The cover is plastic on both the first and second boards. The first on is the SR504-4 and they replaced that with the SR503. Both have fuses for each relay. When I first discovered the issue, I tried changing these first before calling the contractor and nothing worked. Don't understand why they don't put a fuse on the 24v transformer to protect it, but who knows. These pictures include the first board, the second pic is after they came back to replace the 2nd blown 24v transformer and they then put fuses on from the tstat into the transformer and on the other side to protect the 120v coming into the transformer as a temporary fix until the whole board is replaced AGAIN. The boiler is on this same circuit so if it exceeded the amps, I would think the breaker at the panel would trip but it didn't and the boiler never went off or had any issues, only the board itself.

    It is hard wired into the board, no wall plug. Same circuit breaker runs the board and the boiler. According to the contractor, the transformer isn't protected and so he thought the ecobee was the issue and when replacing the first time he put a manual fuse between the ecobee and the transformer. After he left and I spoke to ecobee tech support, they assured me the Tstat doesn't send power back so they convinced me to try it in another room where my 2nd ecobee is to test it. It came right on so they verified it's not the tstat. Took it back to the living rm where the issue started and then the 2nd board popped (That's what I mean when I say the board got fried) Seems the transformer went again but the fuse he put on between the Tstat and transformer didn't protect it obviously so how could it be an ecobee issue? So has to be the 120v coming into the board, right? After he replaced the 2nd board, again blaming me and the Tstat citing I shouldn't have reconnected it, we put the temporary battery operated old Tstat on and it worked overnight fine. I understand this is run on batteries and not the board power but if it was the 120v coming in, wouldn't it have popped the fuse he installed overnight? The supposed faulty ecobee was set up in another room and left on all night, no problems.

    The ecobee is wired in the pic; the red is unhooked in the pic but it was in the Rh and this one only runs heat to first floor only. The two other ecobees run both a/c and heat. Its unique set up b/c we have a boiler running the heat to rads in most of the house except the kitchen is forced air from an air handler that is fed by the boiler via hot water. That air handler also runs the a/c for the kitchen but the rest of the house is high velocity a/c from the third ecobee that it connected to the high velocity unit and the boiler for 2nd/3rd flr heat. Confused yet??

    First pic-kitchen ecobee set up going to air handler. This is where I tested the other "faulty" ecobee and its working fine in this place; kept it here overnight to see if it did anything to the air handler board and no problems.

    Second pic-this is the site of the issue, red was connected to Rh, wasn't connected in the pic.
    this ecobee only runs the heat for the first floor rads and now has the temporary battery run Tstat in place, pic 3 set up

    Fourth pic-this is the current set up with the 2nd board replacement, replaced 24v transformer and he put on 2 manual fuses one in between the Tstat and transformer the other in between the 120v and transformer all is working fine, but the battery operated Tstat is on that line for now

    Fifth pic-this is before it blew a second time with only one fuse between Tstat and 24v which did not protect it and it blew shortly after I reattached ecobee







  • Jamie Hall
    Jamie Hall Member Posts: 22,941
    A few random thoughts...

    It's not the Ecobee. You put it on a different system and it's working fine. So forget that. It is, howver, possible that there is a problem in the wall base -- but the checks I suggested yesterday will help find that, if it's there.

    On fuses. Your panel circuit breaker for the boiler and accessories is, most likely, a 15 or 20 ampere, 120 volt breaker. It is there to protect the wiring to the boiler. It is not there to protect the boiler or any of the boiler accessories and controls, such as the board. Those, if they have any protection will have it as part of themselves -- and for the board in particular it will be a much smaller fuse.

    Protecting a typical 40 VA 120 to 24 VAC transformer requires a very small fuse indeed on the primary side -- 1/3rd or 1/4 amp rating, and it needs to be a fast blow. I doubt that it's there, although some transformers may have a fusible link built in. For troubleshooting, if it's an independent transformer, you can put a 1.5 amp circuit breaker on the output (24 volt) side. If a board fuse is blowing, you may be able to find an equivalent plug-in circuit breaker (same rating) to avoid the nuisance of replacing the fuse; try DigiKey or possibly an auto parts store. There are other approaches, however --and the multimeter is the place to start.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • bucksnort
    bucksnort Member Posts: 167
    Have you looked at the back of the boards to see where there's damage?
    STEVEusaPA
  • Jamie Hall
    Jamie Hall Member Posts: 22,941
    Are we talking about frying the board, or the transformer? Two very different problems. And accurate identification of the problem is the very first step in solving the problem.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • jac34
    jac34 Member Posts: 63
    Thanks, I did not yet check the back of the board, I will do so. The weird part is the first board that died it was the whole board, the second time they were able to just swap the transformer to get it back up and running. Don't know if that gives any hints or not?
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,506
    edited February 2022
  • Jamie Hall
    Jamie Hall Member Posts: 22,941
    It may have been that the whole board needed to be replaced -- but I doubt very much that the whole board fried. What trace or component on it died?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Lance
    Lance Member Posts: 258
    wiring is always a common suspect. Ohm it out, manipulate it work it, pull it, twist it. Until that is done I would not trust it until it passed all attempts at failure. Staples, nails, and wear all overtime will kill the vine. When wired measure the amps. and volts to see how it works. With out knowledge all is a guess.
  • HomerJSmith
    HomerJSmith Member Posts: 2,403
    edited February 2022
    If the whole board fried, like the tracings on the rear, maybe just the transformer, I think I would be looking at a possible 220V getting into it. That would certainly do the trick. It could be 220 V on the primary side. Maybe a short to ground in the electric water heater element as an example.

    What it could be is two interacting devices across the two busses in the circuit breaker box, that would give you 220 V. I would want all Ecobees and boiler controls on the same buss bar in the panel, which may mean re-arranging breakers. Just a thought.

    Was anything else replaced before the problem surfaced?
  • wmgeorge
    wmgeorge Member Posts: 222
    You have a Y1 connected, is there an AC unit connected to the system, that has its own transformer?
    Old retired Commercial HVAC/R guy in Iowa. Master electrician.
  • jac34
    jac34 Member Posts: 63

    It may have been that the whole board needed to be replaced -- but I doubt very much that the whole board fried. What trace or component on it died?

    I only say that b/c when they came out the first time they couldn't even replace just the transformer b/c they said the whole board was dead. They rigged it up just for the weekend until they could get the new board. That limited us to just one zone b/c there wasn't even juice to run all the circulators I'm assuming.

    When they came out Monday to follow up, they replaced the whole board and then the second time they just replaced the transformer which is how it's running now.
  • jac34
    jac34 Member Posts: 63
    wmgeorge said:

    You have a Y1 connected, is there an AC unit connected to the system, that has its own transformer?


    That pic with Y1 is the set up in the kitchen where we tested the supposed failed ecobee. That runs to an air handler that runs a/c and the boiler runs to that for heat in the kitchen (forced air).
  • wmgeorge
    wmgeorge Member Posts: 222
    edited February 2022
    How about a picture of the one your having an issue with?
    I would fuse the 24 volt Secondary, we used automotive fuses 3 amp or so our fuse holder was two quality 1/4 inch spade female connectors, insulated ones or taped. Perhaps you already do this? Used to be able to get 3 amp mini circuit breakers for low voltage... same type of spade connector of course.

    Going to tell a story on my youngest son, the one who does everything perfect. We wired his house, the Right way and he had an issue with just one circuit. Ended up dead ending one outlet in his garage, and he blames the siding installer but someone put a nail in the wiring, but it was NOT shorted all the time. Took him some time to find!!
    Old retired Commercial HVAC/R guy in Iowa. Master electrician.
  • jac34
    jac34 Member Posts: 63

    If the whole board fried, like the tracings on the rear, maybe just the transformer, I think I would be looking at a possible 220V getting into it. That would certainly do the trick. It could be 220 V on the primary side. Maybe a short to ground in the electric water heater element as an example.

    What it could be is two interacting devices across the two busses in the circuit breaker box, that would give you 220 V. I would want all Ecobees and boiler controls on the same buss bar in the panel, which may mean re-arranging breakers. Just a thought.

    Was anything else replaced before the problem surfaced?

    Nothing was replaced, it was all working fine.

    If it was 220v in circuit box, wouldn't it trip the breaker? I'm lost...
  • jac34
    jac34 Member Posts: 63
    Lance said:

    wiring is always a common suspect. Ohm it out, manipulate it work it, pull it, twist it. Until that is done I would not trust it until it passed all attempts at failure. Staples, nails, and wear all overtime will kill the vine. When wired measure the amps. and volts to see how it works. With out knowledge all is a guess.


    I believe the contractor did that but I can't say for sure. Seems it would make sense to test all that, but I can't say for sure.

    I do know he tested the power coming to the wall and it read 28v once the new board was replaced.
  • Jamie Hall
    Jamie Hall Member Posts: 22,941
    A 220 volt misconnection somewhere wouldn't trip a circuit breaker in the switchboard usually -- it would simply fry whatever might be connected to it. Breakers trip on current, not voltage.

    I am rather afraid that it sounds as though you -- or your techs -- are taking the easy way out: keep firing the parts cannon until something accidentally hits the problem.

    You can still get low amp circuit breakers and the terminal adaptors for automotive type fuse boxes. Good auto diagnosticians use them all the time.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Zman
    Zman Member Posts: 7,549
    Both the Taco and the AC have transformers. If those transformers are on different phases and you do not have them isolated, all sorts of crazy things will happen including 48VAC power and smoke coming out of the transformer.
    I am not an Ecobee guy and Ecobee does not seem to publish electrical diagrams so you can see how they actually work but the picture that shows a red wire on Rc and white wire on W1 looks problematic. I would expect that the Taco should be connected to Rh and W1 and that everything else should be connected to the AC.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • HomerJSmith
    HomerJSmith Member Posts: 2,403
    edited February 2022
    jac34-said, "If it was 220v in circuit box, wouldn't it trip the breaker? I'm lost... " Ah, NO. it would destroy every 110 V device connected across the two buss bars.

    If you had a fuse on the secondary of the transformer, regardless of the fuse rating, it would only blow at an over current condition. It would not blow at a high voltage condition, I think. I'm thinking 220 V on the primary side of the transformer, I don't know why.

    Looking at pic 2, what is the black wire going to Rc? You should have Rh, C, and W1 connected.

    Rh and W1 form a circuit thru the switch in the thermostat from the 24 Vac transformer secondary to the relay coil in the Taco. That coil activates a switch in the relay and turns on a circulator. The coil wire output from the relay goes to the common secondary of the transformer. Rh and C form a charging circuit, Rh comes from the 24 Vac secondary to the Ecobee's charging circuitry back to the common secondary of the transformer.

    A short in the secondaries without a load (coil or charging circuit) will blow the transformer fuse wire.

    There is only three things that can blow a transformer, higher than the rated voltage on the primary of the transformer or a short on the secondaries brought on by a direct short or over current operation.
  • wmgeorge
    wmgeorge Member Posts: 222
    edited February 2022
    Add the fuse to the 24 volt Secondary as I suggested... its a no brainer.  If its a 40va start with a 2 amp. Regardless of the over current reason it Will blow.
    Old retired Commercial HVAC/R guy in Iowa. Master electrician.
  • jac34
    jac34 Member Posts: 63
    The tech put a fuse in between the tstat and the 120v going to the transformer. I'm not totally sure on the terminology so pls explain primary/secondary. I believe that is how it is set up now as a temporary fix. Initially the tech installed a fuse only between the Tstat line and the 24v transformer and when I reconnected the Tstat, it blew it again. The temporary Tstat is on there now so i'm afraid to even try the ecobee and lose all my heat. Still waiting on them to figure this out which is why I'm trying to figure it out on my own.

    All the Tstat wiring is correct, it's been set up this way for yrs and working great.
  • Zman
    Zman Member Posts: 7,549
    edited February 2022
    I believe (based partly on your pictures) that you had the ecobee wired incorrectly. What you show in the new wiring is not the same as the old.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    wmgeorge
  • jac34
    jac34 Member Posts: 63
    The first pic is the ecobee in the kitchen-no problem here I just posted that to show how that one was wired running both heat and a/c.

    The second pic is a different ecobee where the issue started. This ecobee only runs the boiler for first floor heat and worked fine since 2018 when the new boiler was installed.
  • Zman
    Zman Member Posts: 7,549
    Heat only is simpler. If you post a sketch of how it is wired or a closeup pic of the taco wiring we can check that it is all correct.
    It is possible that you have a crushed wire and it is shorting out intermittently. Putting a fuse on the individual wires will help diagnose that without burning out transformers.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    wmgeorge
  • wmgeorge
    wmgeorge Member Posts: 222
    edited February 2022
    Your confusing everyone with the multiple pictures of Not the problem stat! Post the picture of the one your having an issue with and the connections. If you have the Common wire like others have suggested wired in the problem stat incorrectly smoke will leave the Taco. If your not blowing the temporary fuse on the 24 volt side of the transformer, its the wrong type or size. If you put a T87 on that zone I am guess all will be fine.... unless like others suggested... you have a nail or short in the wiring to the t'stat. Perhaps even crossed into 120 vac at some point?
    Old retired Commercial HVAC/R guy in Iowa. Master electrician.
  • Jamie Hall
    Jamie Hall Member Posts: 22,941
    "The tech put a fuse in between the tstat and the 120v going to the transformer"

    What? Really? I do hope not There are such things as120 volt thermostats, but you don't have one.

    Look. It sounds as though your tech is clueless. I hate to say it, but I have a feeling that you are also operating way over your pay grade.

    An Ecobee is no different from any other powered thermostat. You need power, 24 VAC, between the R and C terminals. You need a third switched wire -- W --which supplies power to the switched device. That's it.

    Your switched device needs to have a power source, and a pair of terminals -- hot and common -- to run things. It also needs the controlled component -- usually a relay. It sends power to the controlling device--the thermostat on two wires. A third wire comes back from the control and activates the controlled widget.

    This isn't rocket science.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    wmgeorgeZmanSuperTech
  • jac34
    jac34 Member Posts: 63
    This is getting way off topic and the pics are getting things sidetracked here. The wiring was fine and is fine. That’s not the issue that caused the problem. The temporary Tstat is running on batteries which is why it’s not hooked up the way the ecobee was. No power is needed to that older Tstat so let’s move on from that. 

    And I’m not an HVAC tech. I’m a homeowner trying to solve a problem that the supposed professional cannot figure out so I cane here for some guidance. Good to have more than i opinion b/c ecobee tech support is claiming there is no way their Tstat is the cause of a transformer blowing out. The tech is blaming them and I’m stuck in the middle with a large bill that still hasn’t resolved the issue.  Can’t find good help these days so I try to do it myself.

    So please don’t waste my time with rude commentary. 
  • wmgeorge
    wmgeorge Member Posts: 222
    If the wiring was fine, as you say because you did it yourself. Its not your Ecobee seems your problem is solved.
    Old retired Commercial HVAC/R guy in Iowa. Master electrician.
  • jac34
    jac34 Member Posts: 63
    wmgeorge said:

    Your confusing everyone with the multiple pictures of Not the problem stat! Post the picture of the one your having an issue with and the connections. If you have the Common wire like others have suggested wired in the problem stat incorrectly smoke will leave the Taco. If your not blowing the temporary fuse on the 24 volt side of the transformer, its the wrong type or size. If you put a T87 on that zone I am guess all will be fine.... unless like others suggested... you have a nail or short in the wiring to the t'stat. Perhaps even crossed into 120 vac at some point?

    When I posted the pics, I detailed what each picture represents. This is the one that had the issue but once the tech replaced the board he tested the voltage at the wall and got the 24v reading. The red was connected to Rh, just didn't have it connected in the pic. This set up was working fine for yrs on this ecobee. I checked this wiring all the way back to the board and it looks fine, no breaks or contact to metal that I can see.




  • Jamie Hall
    Jamie Hall Member Posts: 22,941
    I'm sorry you feel that we have wasted you time with rude commentary.

    To summarize, the Ecobee is not the problem. You have it running, or so you say, on another base.

    We don't know as yet whether the base plate is, or is not, part of the problem.

    We are assured that the wiring is perfect with no faults.

    We have no clue as to what failed or shorted to cause the transformer to fail, nor do I see any evidence of systematic diagnosis.

    We have no clue as to what failed on the board, never mind what caused the failure, not do I see any evidence of systematic diagnosis on that.

    If that summary is rude, I apologise. If it is incorrect. please correct and we will try to get further.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • jac34
    jac34 Member Posts: 63
    Yes, the ecobee is running on an air handler and working fine. The tech says that could be b/c the transformer on the air handler is larger and able to handle it hence no problems. Again, he keeps going to the Tstat as the problem which ecobee and I both disagree. He keeps going back to the fact that the battery operated Tstat is having no issues (isn't connected for power) as a temp fix and the problem only reoccured once I put the ecobee on and it blew out the transformer a 2nd time. But yet, it works in the other room...go figure...

    Ecobee says the base plate can't be the problem; it only connects the wires to the ecobee and if it wasn't functioning, it wouldn't even power on and wouldn't short anything.

    I just disconnected the wiring on both ends and tested it with multimeter and don't see any issues; but again, I don't do this for a living nor am I an electrician so I'm not totally sure. Disconnected the wire on both ends and put the probes on and got close to 0 readings. Red to red, white to white, blue to blue, green to green. Do you need to test one probe to one color wire while the other probe is touching another color wire or just same color end to end?

    And I may not be answering all your questions fully b/c I didn't do the work, the tech did and I'm only relaying what I gathered from him. He indicated today over the phone that it was the low voltage transformer that failed each time, not the whole board. But b/c the transformer is soldered onto the board, you have to replace the whole thing. You can replace just the transformer which is how it is rigged for now, but that is not a clean way to do it and they don't want to be liable if something goes bad so they swap the whole thing.