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I’d like to know if I can replace my 2 wire non digital (hot water baseboard heat, oil fired) thermostat with a 7 day programmable thermostat from Honeywell. I’ve tried looking at the www.yourhome.honeywell.com site but they don’t actually show you how many wires are on the back of the unit I want to install (RTH8500D). I want to buy the item from ebay because I can save myself about half the cost, but I also cannot return it if I buy the wrong thing. Anyone have any suggestions?
November 29, 2009 at 12:44 pm
I’ve installed several of these stats.
You can wire a 2 wire system to this stat. If you have an extra wire in the bundle, it is usually better to use it and tie it to the 24 VAC common side at the boiler transformer so you’re not fully battery operated at the stat. That way, the battery is used for backup power instead of normal power.
But just wire the new stat just like the old stat, use the “Conventional” terminal strip wiring (as opposed to the “Heat Pump” wiring) and you should be fine. R to R and W to W.
If you have the extra wire and are capable of hooking it up, use the C terminal on the stat and hook it up to the common side like I said above.
Hit this link: http://customer.honeywell.com/techlit/PD…
It is a PDF instruction sheet.
November 29, 2009 at 1:05 pm
I went through the same thing, The instructions that come with the new T-Stat will explain pretty well…. You simply leave the bypass or jumper in place & wire it exactly like your old one.
November 29, 2009 at 1:31 pm
There are many different models of t-stats depending on how many wires you have. Sounds like you’re better off buying at a store. Sorry
November 29, 2009 at 1:34 pm
First make sure that it is a 24 volt control system that is installed. If you do have a 24 volt control system then it should be no problem ( I say should be because I dont have much info on your system). The t-stat that you have now will have two wires. If you purchase a new t-stat it could have more places then just two for the wires. Just make sure you know which wire goes to R and which one goes to W. Sometimes the old T-stat wire isn’t color coded. If you have standard T-stat wire then the red wire should go to the R terminal and the white wire should go to W. Just make sure that you look to verify this is correct on what you have now.