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Discussion Starter · #1 ·
I have my relay set up as you can see in the diagram. I followed grayfurnaceman's video on Youtube but he used a 90-370 relay so I'm not sure if I managed mine correctly.

The original idea was to finally get my Nest working with a C-wire. It unfortunately did not work. I believe my Nest has other issues now (it won't even turn on when plugged into the wall via USB). However, I put my old Honeywell thermostat back on without batteries, and it doesn't turn on either. I put the batteries back in and everything is working normally. Is there something wrong with my set up? It's odd that everything except the C-wire still seems to be working.

Thanks for any help.

PS - anyone have any luck getting a new Nest out of warranty? It sat on my shelf for 2 years before I got around to this C-wire install and now Nest just says they can't replace it because it's out of warranty. Thanks Nest, it was your fault in the first place....
 

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I'm not sure which video of his you watched (there are a lot), but the relay won't fire because you need to have 24vac at it. Right now you are only running one side of the transformer to the relay. You would need both the R and C wire to the relay which would give you the 24vac to fire it. A link to the video you watched would help tremendously.

As well, the relay you have has two separate poles, as opposed to one form C relay in the 90-370, so the way you have it connected won't work either, because there is no common pole, so it won't switch between the two positions, they are independent of each other.
 

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I redid your drawing for you. I believe this is the only way it can work....

edit.... The terminals on the transformer sometimes aren't labeled. It they aren't, it doesn't matter which one you pick to be "R" and which one you pick to be "C". All I know is they shouldn't be labeled R & W like the one in your drawing.
 

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By the way, where exactly is this transformer that you are adding, and why? If you have enough wires going between the stat and the furnace, or if you have a way to add another wire, the picture below is the preferred way. No extra transformer or relay needed.

Unless your furnace is about 100 years old, it already has a common. I'm literally talking about 100 years old, as in the kind that used a power pile and a milivolt gas valve with no blower motor or any other power going to it.

To find your common (if it's not already labeled) find the transformer that's already in the furnace. The "R" should go to one side of the transformer. The other low voltage side of the transformer will be your "C". The "C" wire is also usually attached to the metal and/or ground.
 

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Discussion Starter · #7 ·
I know I have heard all the bad things about the nest and obviously my issues are bringing that to light, but being $200 invested in it, plus having many other Nest products has led me to be a bit stubborn about it.

I have a Honeywell Triple Aquastat Relay Type L8124A, C - the research I did said that I would have to connect to the hot side of the coil, which is the back side and would essentially require taking it apart and is beyond my limited skill set. Instead I just spliced into the service switch box and sat the transformer on top and then got the relay to help create a C wire.

I researched his video a bit more and he's actually using a White Rodgers 90-290Q which gives a better explanation of why I was confused. Watching it again, I think where you have the C going to the thermostat and then to 3, he has it going from the transformer to 3, and then up to C on the thermostat, which if I'm not mistaken is doing the same thing but with my current wiring set up his way would be easier for me. Here is the specific video I watched:
 

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Discussion Starter · #8 ·
Just letting everyone know that this ended up working, for now at least. Oddly enough, the Honeywell thermostat screen never turned on without batteries in it. However, when I hooked up the Nest it recognized the C-wire as having power and as I said it's running fine.

I realize my situation with the furnace is obsolete, but this solution worked for not being able to access the coil on my Honeywell Triple Aquastat Relay.
 

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I'm glad to hear that it's working out. What you have is a unique situation for sure.

For future reference though, please quit calling it a furnace. What you've got is a boiler. Yeah, I know technically your boiler doesn't actually boil anything, but when you say furnace, most people will assume that you have a forced air heating system.

Anyways, sorry for yelling at you. I'm glad it's all working now. :)
 

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Discussion Starter · #10 ·
Ha yes you're absolutely right it's a boiler not a furnace. I honestly think it's just because I group up in a house with a furnace so it's just muscle memory to call "the thing that produces heat" furnace. I will hopefully catch myself on that going forward more.

Thanks for the help with everything!
 
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