We have a thermostat that only has 2 wires, red and white coming out of the wall, and we want to change it to a digital thermostat with slots of W2, G, E, Y, C, B O, R or we also have a unit that has slots W1, G, Y, C, B, O, R

So my question is this: Are we able to use either of the 2 new thermostats in place of the current ugly one we have?

If you only have two wires it means you have heat only, no fan on/auto or cooling. Hook up the red wire to R or Rh and the white to W1. That's all you need to do.

Read the directions. Some may require the common side of transformer to be connected to the C or B terminal. Many don't

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Originally Posted by labman

Read the directions. Some may require the common side of transformer to be connected to the C or B terminal. Many don't

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Just C (common) Blue is for Rheem/Ruud/Weatherking heat pump reversing valve, Orange for about all other makes of heat pumps

Well, I hooked the red wire to the R terminal, and the white wire to the W1/W2 terminals on both units and no luck. However when I hooked the Red to R, and the White wire to C, OR the Red wire to B and again the White wire to C, it displays, BUT the heater doesn't turn on? The instructions don't tell how to hook up a two wire(red/white) thermostat. Anyone know where to put the red and white wires into the terminals? On another note, the instructions kept mentioning that multi stage thermostats shouldn't be used on single stage units... maybe this is the problem.. how do I know if I have a single versus multiple stage unit?

Chances are, if only had 2 wires originally, you have a single stage furnace. Look at it. If it just has a W terminal and no W1 or W2, it is a single stage furnace. Even if like mine, it could be wired as a 2 stage furnace, you will have to continue to run it as a single stage unless you run a cable with more wires.

NorthernHeat, you rule! I just struggled for about 2 hours wiring and re-wiring my new thermostat--didn't work until I read your simple R/Rh and W1 instruction above. The Honeywell directions and website were about as useful as a cookbook would've been. Thank you!!

+1 for NorthernHeat - THANK YOU! Worked perfectly!

+2 for northernhear --- Got two thermostats in my house working. Thank you for the help :)

I also have a 2-wire setup. Do I need a battery powered thermostat? Because Rh and W1 don't seem to work for me on the new tstat.. screen is blank.. no lights.. R and W1 work on the old tstat, but its battery powered. Thanks!

Hi there I need help with my room stat. it is very old with only 2 terminals red and yellow and I'm getting 12v down either red or yellow. I have a blue cable there as well but isn't connected. The new stat which has 4 terminals which are 2, 1, N, N. on the wiring diagram it shows to only use live in 1 and neutral in the first N but which cables do I use? *** help me?

In a 2 wire system u also need to check the voltage
Mostly stats works between 20-30Vac or 750 milli volts but some stats might not work on 750 millivolts
In 2 wire system we require battery power stats.

I have a gass furnass and neather of my two wires were color coded or marked so he told me the wire that goes to the murcury bulb goes to "r" and the wire that goes to the spring goes to "w". And if it does not work then just switch the wires. And the stat I hooked up was from the old simple style to the rth6400d stat. hope this helps anyone.

NORTHERN HEAT ROCKS!! I have been looking for this answer ALL DAY!

I hooked my 2 wire as follows: red to R and hooked white to G(its the fan switch). Make sure your fan switch on the thermostat is on AUTO. Adjust temp, Let it sit, it takes a few minutes to kick in, and presto. I have a old 2 wire heater/AC, u know the mobile home kind, that if I want AC I have to take cover off and flip the switch then put cover back on. Im using a T1040 battery powered stat. it works great!

I want to replace a honeywell two wire thermostat to a hunter thermostat it has G RC RH Y/O W/B Y1.. the wires coming from the wall are red and white. I have heat and ac with the old one I put the new one on there and the heat will work but the ac will not can someone please help me out.. I'm about to loose my mind...

Hi
None of the digital stat will work
Need to get Honeywell CT30A.
Because u have 2 wire heat and AC.

Did exactly as you said and worked thank you very much

I have 2 black wires which were attached to an old mercury thermostat. I have a new Honeywell digital thermostat I would like it to connect to. How can I determine which letter code to connect them to?

NorthernHeat = #1

Thanks for the help. Saved me a lot of time and curse words!!