Another Smart Thermostat Question

MrVince · January 16

Hey, Guys!

I'm sorry but I have to ask another smart thermostat question. Last year, I followed someone's diagram. It's hazy but I remember that it wasn't the optimal solution, but it did work.

However, for the past few months, the thermostat gradually got worse. First, it would occasionally turn off by itself. And, now, for the past month, it happened even more frequently. Starting from yesterday, the smart thermostat reboots about a minute into the heating cycle.

I'm guessing that my c wire is connected to something that drops in voltage immediately after the heat turns on. (I'll go test it in a minute to confirm but wanted to post this question first.)

For the past hour, I've been scouring this forum to find the correct solution, the one that has a constant power source. Does anyone know which one it is or can tell me what I need to do?

This is my equipment:

Weil McLain EG-35
ecobee Smart Thermostat Enhanced
transformer

I have a transformer but I ended up never using it last year. I'm not sure but I think I followed this diagram from a post here.

I pretty much followed this diagram. I even plugged the common wire into a screw in that exact location.

I guess my first question is whether this is a C wire issue and not something on the boiler side. I checked the boiler and it doesn't seem like it.

Can I simply plug the c wire into something more stable? Or do I have to use the transformer to provide a steady power supply?

MrVince · January 16

I checked the voltage with my multimeter.

The R-C line stays constant at about 27.9V before the call for heat, during the call for heat, and after the short cycle.

The W-C line is about 2V before the call for heat. During the call for heat, it goes up to about 27.8V. When the boiler short cycles, the voltage drops to about 4V.

Given the numbers above, am I right that the thermostat is broken?

What's strange is that it seemed that the boiler would cut off when there was the slightest heat/pressure built up. So I was worried that a pressuretrol was broken or something and it was setting off a short cyle. But if that's the case, the voltage on the R-C line would drop, right?

Since the R-C line's voltage is always constant, the thermostat must be broken, right?

Jamie Hall · January 16

Thermostat may or may not be broken. R-C should always be about 24 to 27 volts, so you are good there.

MrVince · January 16

https://forum.heatinghelp.com/discussion/comment/1882592#Comment_1882592

Jamie,

Can I ask you a quick question? Right now, my house is 60° because of the short cycling. Can I just connect the R and W wire to call for heat? Then when the house is all warm, just disconnect them?

Just want to make sure I'm not going to short anything. I know I can't jump the R-C nor W-C. I guess I'll just turn off the power, then connect R and W with a wire, and then turn it on?

This will also definitively prove whether it's the thermostat or the boiler.

MrVince · January 16

I guess nobody is back home from work. ☹ It's ok. I'll just talk to myself. 😃

I jumped the R-W line so the boiler just turns on indefinitely. I'm such a newb that it took me an entire day to think of this. The house is finally getting warm.

I'm thinking this result demonstrates that the boiler was fine and it was definitely the thermostat. The only other possibility is loose wires between the thermostat wires and the thermostat. Since they weren't loose, I'm guessing it definitely was the thermostat.

I've been on hold waiting for an ecobee rep for hours, so I can file a warranty claim. Before I bought this, I read a lot of complaints about ecobee's customer service. They weren't lying. It's hard to get through. And when you do, they jerk you around because they don't want to send you a replacement.

Enjoy the weekend, folks!

EBEBRATT-Ed · January 17

That may be an @EdTheHeaterMan diagram. It's too good to be one of mine.

EdTheHeaterMan · January 17

@MrVince That is my diagram. I need to know if you used Rc or Rh for the Red wire from the R on the transformer to the R wire on the Thermostat. The thermostat needs to see 24v. at Rc and C to operate properly. If you used Rh because it is for your heater you may have a problem. The only time you use Rh is if you have a separate air conditioner with a separate air handler transformer. Then the Rc and C comes from the air handler transformer. Does your thermostat also operate your air conditioner?

If you are using Rc and W and C on the thermostat, for heat only, then there is one more test to try to rule out the thermostat. I have moved the thermostat on the diagram to make the test clear. I am guessing that you jumped R and W at the boiler location as in the A position on the diagram. Now try the B position on the diagram. Put the wires back the way they were and put the R to W jumper on the terminals at the thermostat location upstairs. That test will rule out the wiring between the thermostat and the boiler.

Screenshot 2026-01-17 at 12.23.37 AM.png

I also want to say that the diagram shown is not the way it is on the boiler or in the manual. The LWCO is connected a little differently. It is described in the red text in the lower right corner. You said "I pretty much followed this diagram." I would rather you say "I followed this diagram exactly. If you did not follow that rewire and then test the LWCO and all the other safety and operating controls to be sure they are operating properly, then you need to double check every connection from one end of each wire to the other. Also make sure the factory installed jumper from 1 to P1 on the LWCO is removed.

I hope this helps.

Another Smart Thermostat Question

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