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

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

Errr what if both wires are red?

Hi, I have an old 2 wire Taco analog thermostat and want to upgrade to a digital thermostat. The wires are white and blue (the red wire is cut and not connected to anything) and neither terminal is labelled. Any suggestions on how to wire new device?

Thanks

Connect one wire to Rh & the other to W on the stat. Use a battery powered stat.

Is it just me, or did NO ONE answer the question on how to hook up a 2 wire setup to a digital (no battery) thermostat; which I thought was the original question?

Yes, 2 wire = Rh+W great... what about hooking in a WiFi digital thermostat? Feasible or not? And if yes, how? (regardless of wire colors which can't be relied on)

Any suggestion would be very welcome. Thanks.

Thank u it worked very well..

Thank u for your asvice. It worked very well and I'm very happy. Hoping it will help with my power bill..

thank u for your asvice. it worked very well and im very happy. hoping it will help with my power bill.....

We are trying to replace an old school thermostat with a Honeywell 5-2 programmable thermostat. When we took off the old one, the wire we have are as followed: romax with red/white and another set of romax that has no colors. When we connect all the wire as we think, it causes the furnace to run. When we switch it to A/C, every thing works. Can you tell us how to hook it up?

It Didn't Work, one of the Wires was feeding off another to serve as a C wire, I called HoneyWell and they said their updated wireless thermostats will not work with my two/3 wire system unless I have an entirely independent C wire running from the heater -_-

Buying a home with an interlink furnace. Pilot will light but burner will not ignite. There has been no gas in the home for over a year. Line was purged, pilot lit, thermocoupler kept pilot lit. However the main burner won't light. Supposedly the furnace worked in Sept. 2012 when gas company came out and lit pilot. HELP!

Tattoo:
Are you sure the gas valve is set to "on" & not "pilot"?

Yes. The gas valve was set to on after lighting the pilot. I am assuming you are talking about the knob on the gas valve that controls the pilot and burners. Atl Gas was trying to light it and I attempted to as well after he left. Same result, pilot lights and stays lit. Turn the knob the rest of the way and nothing happens. This was with the thermostat turned to 90 degrees, house was about 60, fan in auto and switch set to heat. Tried the cool side of the thermostat thinking it may have been wired backwards but to no avail.

Ok, you've covered some of the common mistakes.
If you have a voltmeter & know how to use it, measure voltage at the thermostat. You should get +/- 24 volts AC between terminals R & W. If you do, put the stat back on, set it for heat & turn it up high. Measure voltage between R & W at the furnace. You should get nearly nothing.

My new one has batteries as well, and no W1 or RH. It does however have a R and W hookup. Hopefully I get this thing to work, it's starting to get a little chilly in the AM...

Im replacing my old honeywell round thermostat (with Mercury) both wires are the same color... What do I do??

mommynkiddos: hook one wire to 'W' & the other R. It makes no difference which is which.

This may be the wrong place to ask, if so I apologize, but, with new wiring and an appropriate relay, can one convert a mobile home style gas furnace, with the heat/cool switch on the blower, to work with a newer stat? I don't mind running new wires or setting up a transformer inline if needed, but do not want to spend what I was quoted on a new furnace.