Question about Honeywell Programmable Thermostat Heater

1 Answer

Hooking up new thermostat to new furnace

I have a honeywell rth7500d thermostat. i have the G Y W R hooked up and the thermostat is not on. i have a blue wire also not hooked up. it is not hooked up in the furnace either. should this be my 24 volt supply and where do i hook it up in the furnace?

Posted by on

  • nwendtibc Jan 23, 2009

    what about "B" and "O"
    i hooked up the blue wire to c on the furnace and to b on the thermostat and the low volt fuse blew. the furnace instructions said to hook up c on furnace to b/c on thermostat for 24 volt. i am trying to power the thermostat so i don't have to change batteries and reprogram.

  • nwendtibc Jan 25, 2009

    What if a digital t-stat does not have a "c" terminal, but you want to keep it energized with 24 V? How is that done?


1 Answer

  • Level 1:

    An expert who has achieved level 1.


    An expert that hasĀ over 10 points.


    An expert whose answer gotĀ voted for 2 times.

    Problem Solver:

    An expert who has answered 5 questions.

  • Contributor
  • 12 Answers

Letter designations for honeywell tsats R=24 volt power, W=heat, Y=cooling, G=fan, C=common wire for the 24volt power to tstat. Generally R is the red tstat wire and so on. Blue tstat wire can be hooked up to common at the tstat. On the heater the blue tstat wire would be hooked up to the C terminal. But this also depends on the manufacturer of heating unit.

Posted on Jan 22, 2009

  • 1 more comment 
  • HVAC TECH 2 Jan 24, 2009

    The O terminal is for heat pump reversing valve being energized in the cool mode and the B terminal is for reversing valve being energized in heat mode. If rev. valve energized from O tereminal for cooling and the coil were to fail it would failsafe to heat, and just the oppisite if B terminal energized and rev. valve coil would be failsafe to cool. Rheem & Rudd are tippically the only manufacturer that energizes the reversing valve off of the B terminal in a residential application.

  • HVAC TECH 2 Jan 24, 2009

    Follow up on the wiring, when you hooked the blue wire to the C terminal at the furnace you should hook it up to the C terminal at the tstat. The previous message I explained the O & B terminal. If you have a gas furnace you should hook up to C terminal. Also, did you get into the installer setup to set your thermostat up for your system. This thermostat is compatible for multiple systems. If this does not answer all your questions check out and on the home page on the right side of page 3 gray boxes, enter tstat # and click on the box to view installation guide to navigate through the installer setup. Hope all this helps!!!

  • HVAC TECH 2 Jan 26, 2009

    Everything that I see on the internet the top left should be the C terminal which is common to operate tstat without batteries. If your tstat does not have a C terminal then that may be a design change that has not been upgrades on the internet. Check out this web address Grey box labeled literature put tstat model # in and select above the model # highlight installation manual. If this does not help I will call honeywell on monday.


Add Your Answer

Uploading: 0%


Complete. Click "Add" to insert your video. Add



Related Questions:

1 Answer

How to turn on my honeywell thermostat

Your thermostat should power on without a problem if it is battery operated, and even then, when you put batteries in it, it should still power up. Without knowing the exact model, the only other problem I can think of, the power to the thermostat is supplied by the furnace which is a common wire (usually blue) that is also hooked up to the C terminal on the thermostat. If there is a common wire hooked up, then you have to check if you have power to the furnace. If not, the problems could get more complicated. Hope this helps.

Jun 15, 2010 | Honeywell Programmable Thermostat Heater

1 Answer

I install new RTH7500D thermostat Honeywell, when I set for Cool it blowes heat when I set for a Heat nothing works I wire per instruction have two stage system

It sounds like the t-stat is programmed for a heat pump or you have a heat pump and the t-stat is programmed for a regular furnace....
Check out the manuals in the tip and go into the installer setup to change the t-stat to the proper programming for your system..


Apr 24, 2010 | Honeywell Programmable Thermostat Heater

1 Answer

I'm replacing an old thermostat with a new Honeywell RTH6300B programmable. I have propane heat and central AC. My old thermostat has a black, a red and a yellow leads with no ID on the old thermostat wall...

Open up the propane furnace and see what color wires are hooked to the gas valve or circuit board. If it has a circuit board, note which color is on the R terminal and W terminal, Connect the the thermostat the same way. Most likely the yellow wire powers your A/C so you can hook that one to the Y terminal.

Nov 27, 2009 | Honeywell Programmable Thermostat Heater

1 Answer

One honeywell to another

you need to program the thermostat for the reversing valve "O" it will tell you how to do this in the manual. you will need to chang from "O" to "B" or "B" to "O" depending on how its set.

Jun 24, 2009 | Honeywell Programmable Thermostat Heater

1 Answer

Updating old honeywell thermostat with a new honeywell thermostat

check in the unit heater to see what is hooked up most only need to have red from transformer white to call for heat and green to make the fan run in man and somtimes common usually blue or black

May 09, 2009 | Honeywell Programmable Thermostat Heater

1 Answer

Old mercury thermostat, New furnace wiring issues

Two wire hookup on the old thermostat tells me that it was set up for heating only. You will most likely need a modern thermostat. But in the meantime try this with the old one. The two red wires on the furnace are probably Rh & Rc. If so these can be put "together" on the R terminal on the old stat. The two W's on the new furnace are probably W1 &v W2 This is for first and second stage heat. You can put the two "together" on the W terminal on the old stat. Do not hook up the greens (blower fan wires). Do not hook up the blue wires (They would go to the Y terminal on a modern stat for airconditioning.
Who ever sold you the furnace should have offered you a new thermostat.
Good luck....

Mar 29, 2009 | Honeywell Programmable Thermostat Heater

1 Answer

RTH2520B Honeywell Programable Thermostat wires

Hi soozankrayg!
Your problem should be pretty simple. (assuming that it is a typical 24volt system) you should hook up the black wire to the "RH" terminal and the white wire on the "w" terminal. Make sure that you turn off the power to the furnace at the breaker or the furnace itself before attempting this. The reason for this is that you can cause a short and either break the fuse at the furnace or burn up the circuit board. This can happen very quickly and is very common when a thermostat is removed.

Jan 28, 2009 | Honeywell Programmable Thermostat Heater

1 Answer

Install a digital Honeywell thermostat

What kind of system do you have (furnace with heatcool, heat pum or boiler )? Is there a themostat there now. How many wires does it have. If you have a furnace and you have heat&cooling install red wire to r on thermostat white wire to w and green wire to g. The g wire is usually for the fan. If there is a thermostat there now the old one should have the same letters on the back by where the wires hook up. The color of the might be diffrent than the ones i used for an idea.

Jan 17, 2009 | Honeywell Programmable Thermostat Heater

1 Answer

Turns on and Turns off

Does the furnace burners light? You could have a bad thermostat or a flame sensor. To check if it is thermostat turn power off to furnace take thermostat off wall take wires marked r & w and connect them together then turn power back on. If furnace comes on and stays on then you need a new themostat if not it is the flame sensor inside furnace. Also check furnace filter

Jan 13, 2009 | Honeywell Programmable Thermostat Heater

2 Answers

Honeywell thermostat

If you have a forced air furnace with an air conditioner attached make sure you have a jumper wire between Rh and Rc. If the Bryant thermostat had a wire hooked up to C you do not want to hook this up to Rc. Just cap it off and put it back in the wall or disconnect that wire down in the furnace.

Aug 10, 2008 | Honeywell Programmable Thermostat Heater

Not finding what you are looking for?
Thermostats Logo

Related Topics:

3,387 people viewed this question

Ask a Question

Usually answered in minutes!

Top Honeywell Thermostats Experts

Bill Long

Level 3 Expert

577 Answers


Level 3 Expert

1898 Answers

Brandon Berry
Brandon Berry

Level 2 Expert

407 Answers

Are you a Honeywell Thermostat Expert? Answer questions, earn points and help others

Answer questions

Manuals & User Guides