Not totally sure how to upload a picture but it’s two copper wires, one has blue cloth/wrap and one has white. The thermostat is hooked up to a old Honeywell mercury thermostat and is connecting to the boiler (baseboard radiator heat). Thermostat is heat only.
Laurentbourg, I have exact same setup which is Honeywell mercury 2 wire to boiler baseboard heater. I have the Nest Thermostat (NOT LEARNING). I also purchased the 120V plug-in transformer which has 2 wires. I think I have to wire that to C and also with R? This means I have a wire from the boiler control board to R and also the transformer to R. Is this correct?
Thanks for posting and sorry for the delay.
Chiming in to see if you still need assistance with this. Hope the previous post helped. Were you able to setup your Nest Thermostat?
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Hi this is very similar to our current setup we just installed the regular nest thermostat tonight to an old boiler oil heater radiator system that just has two wires a red and a white so we connected them to the r and the w connectors. I was able to set up the app and set a schedule for the heat which is all we have there is no cooling) but within 5 or 10 minutes of starting it said that we needed a c wire or a nest power connector which frankly my husband does not want to deal with. I'm getting confused on how to just have it set to turn the heat down when we go to sleep and turn it back up in the morning 7 days a week. Can I just do that from the thermostat itself? My app says it's connected to the Wi-Fi and so does the thermostat. Sorry I'm so confused at this point any help you can give me will be appreciated
We used a 25 foot length one because we plugged it in the basement receptacle and went up to first floor to the thermostat. This should fix your problem and depending on which Nest you have the wiring might be a little different.
Thanks Scuba Shawn, that looks doable. The wiring diagrams being different in our old house from what is pictured in the best instructions has been frustrating, but with just two wires, we simply connected the red wire to "R" and the white wire to "W/Wh". I'm not sure where the c wire would connect if we got this unit you're recommending because so many of the instructional videos do not deal with a system that is not an HVAC or that only has two wires. Which terminal did you connect to your c wire to? Thanks for the product idea, I wasn't sure if it was only compatible with Google products(and personally feel that Google should give those kits to any consumer since they haven't made it compatible with this kind of heating system, which is very common in my area. I guess I'm still pretty frustrated that what was supposed to be a simple install is turning into a pia). Thanks for your help.
Hello Skymom, I am assuming you have the newer Nest Thermostat that has only 6 terminal blocks where it is Y, C, and W on the left and G, R, OB* on the right. If so, then you are correct in that you have the 2 wires on R and W. I am not sure where you see Wh but maybe that is a different stat than the newer Nest Stat. The transformer that I linked above will give you the needed C wire to help power the stat. Those 2 wires go on R and C. this means you will have 2 wires going into R. Just make sure the striped wire on the transformer goes to C. It should be that easy.
Hi scuba Shawn,
Thanks for this your idea seems like the easiest and I'm going to try ordering that today. We have an outlet right near the thermostat so I won't need the 25 ft but we'll just keep it wrapped up.
In the meantime it's reading that the battery is already low even though we just installed it yesterday. Is it truly low or is that just getting confused? I can keep changing batteries out everyday until we get the new unit I just wasn't sure if it was accurate.
Thanks so much for this simple fix!
Glad I could help. You can cut the wire shorter if you don't need so much. See if there is a way to hide the wire in the wall if you want to really hide it. Yes, the battery is probably dying quickly but I would let it die completely before replacing.
PS: Please post a picture of the wiring on the stat when completed as it might help others and confirm what we think you are doing. Good Luck!
Hi Skymom, typically hydronic boilers are multi-zone and use controllers that thermostats feed into, so if you see a big green box with Taco written on it somebody handy should be able to easily add a C wire to your system.
Hi Laurent, it is only one zone. An oil fired boiler with one control in the center of an old house. No HVAC. Just heating the water delivered to the old cast iron radiators, to heat the house. It's an old system in an old house but we did check compatibility before we got the nest and it said it would work with the two wire system. However now it seems to want us to install a c wire which is really not compatible with our old system. Does that make more sense? I appreciate your help but your last response did not seem to apply to us. thank you
okay I think I've gotten some good pictures here of what's coming out of the wall in the one thermostat that's in the middle of the house, end of where they connect to the boiler. You have to follow the old cloth covered wire to where it divides into the red and white. We've taken a picture with a finger behind the appropriate wire so you can determine the correct red and white wires. Hopefully that makes sense and that these pictures are going to make everything crystal clear so that all of you very helpful people can help us figure this nest out. Thank you.
ok thanks. Yes it is normal that A2 already has a wire, it is the common from your boiler transformer, which is what C is, you need to piggy back on that connection. If you don’t mind exposed wires or amateur solutions you can use a transformer plugged into a wall into your Nest but I do not recommend this. I would just ask a handy friend to fish a new wire connected to A2 into your Nest.
The only thing you need is thermostat wire with 3 wires long enough to go from your boiler to your thermostat (it’s called 18/3 wire, https://www.homedepot.com/p/Southwire-50-ft-18-3-Brown-Solid-CU-CL2-Thermostat-Wire-64168840/2048622...). You can use your existing cloth wire to fish the new one, a handy person will know how to do that. I am not sure what you mean by the Nest connect kit, can you please send me a link?
I guess it's called the power connector. What's confusing me is it says you can either install a C wire or get the power connector but when I've been reading about the power connector and how to install it, it is assuming we already have a C wire. So it was beginning to sound like we need both?
But I think you're saying that if we just install a C wire that should do it.
The C wire in your system is the A2 terminal. So if you have a third wire in that old cloth you can connect it to the A2 terminal, and then use that wire on the thermostat side. If you don’t have a third wire, then you need to connect a new wire to A2 and find a way to bring/fish it to your thermostat, which can get involved depending on the location of your thermostat in relation to your boiler.
Yes it's really way too complicated to deal with and it seems wrong to have to hire a professional to do what was supposed to be a simple home install. If you'll notice there's also already a wire attached to A2. I'm not sure how they would interact?
And scuba Shawn was correct earlier and stating what the terminals are labeled as. I've been looking at so many wiring diagrams that they have frustratingly made different in all of their thermostat units that are available now so I got that part confused.Unfortunately it's probably not going to look pretty to have a wire running down that wall but right now I just want a functional thermostat.