Plumbing, Electrical, & HVAC

Honeywell Thermostat Wiring Instructions

If in the market for a new Honeywell thermostat, make sure you understand your Honeywell thermostat wiring needs before upgrading.

Q: I installed my new programmable thermostat, but it won’t turn on.

A: If you plan to upgrade to a new thermostat make sure you have the proper number of wires available, otherwise your new thermostat won’t work. If you do need additional wires, you will want to consider how difficult installing new wires will be for your application.

Modern electronic thermostats are no different from any other technology, in that they can do more, but can also seem complicated to install and understand. One comfort to know is the basic wiring hasn’t changed much, with exception of an additional wire to get some programmable digital thermostats operating.

Note: For specific thermostat model installation manuals and wiring instructions, refer to our Thermostat Buying Guide for a complete list and link of manufacturers. Individual thermostat model information is most likely the best place to find particular manuals, and not a general manuals category that can be found within the search function.

SEE ALSO: In-Depth Thermostat Wiring Explained
SEE ALSO: Heat Pump Thermostat Wiring
SEE ALSO: Manufacturer Thermostat Installation Manuals – manuals online or manualslib

4 Wire Honeywell Thermostat Wiring

  • G – Fan (green wire)
  • R – 24 VAC / Rc and R or Rh (red wire)
  • Y – Compressor / air conditioner (yellow wire)
  • W – Heat (white wire)

Note: A previous installer may have used a different set of color wires. This will be a non issue to keep track of if a whole new set of thermostat wires is pulled. Otherwise tag the wires before removing from the existing thermostat, or take note of the terminals each wire is attached to.



5 Wire Honeywell Thermostat Wiring

Some programmable thermostats (e.g. Honeywell Prestige wiring requirements) need a minimum of 5 wires, and maybe more depending on what features you want to operate (humidifier, etc). The additional 5th wire will be for common (neutral), which acts the same as it does on an electrical light switch to complete a path and provide power for the display, closing switching relays, etc.

  • G – Fan (green wire)
  • R – 24 VAC / R and Rc (red wire)
  • C – 24 VAC Common (color can vary per manufacturer – may be blue, purple, brown. etc.)
  • Y – Compressor / air conditioner (yellow wire)
  • W – Heat (white wire)



Furnace Electrical Board Connections

Going into your furnace may sound intimidating, but if you have the basic knowledge of wiring, and know how to remove the proper furnace panels to access the electronics, then you should be fine. The COM 24V terminal will be connected to the C (24 VAC common) of the thermostat.


How to Install Thermostat Wire

If you have easy access to the existing thermostat wires, just remove and follow the same path with the new set of wires. You can use cable ties, electrical tape, or staples (securing wires and cables article). Be sure to take a very conservative measurement on how long your new set of wires should be. You don’t want to start over, if you come up short. Any home improvement store should carry thermostat wiring. Also check local electrical and lighting supply houses.

If wires pass through a floor and up into a wall cavity before reaching a thermostat. Try the following.

  • Start at the thermostat location. (i) A simple trick for pulling new wires to replace existing ones: tape one end of the new wires to the end of the existing wires coming through the electrical box or wall opening. Make sure to tape completely over the wire ends, so no edges are present that can snag something. (image below)
  • Slowly pull the new set of the wires down through the wall from the basement. (i) Use any object larger than the hole in the wall, and tie or fasten to the end of your new wires, so you don’t pull all the wire through the wall. e.g. pencil or flat washer, to act as a stop. Use electrical tape to secure if necessary.

In a situation where the original thermostat wires may have been stapled to an interior wall stud, and not run through conduit, you may be better off leaving the existing set of wires, and cutting them off at the entry and exit points of the wall. Then feed new wires with a fish tape (Klein Tools). Check your local home improvement stores, or local tool rental, for rental availability.

CAUTION: ELECTRICAL HAZARD – Always turn power off before performing any work. Contact a certified HVAC tech if you don’t feel 100% sure of your DIY capabilities.



  1. 1

    Hi Shannon,
    I’m going to refer you to this article since you have a heat pump. I believe you’ll find clarity in how a heat pump works compared to a furnace and air conditioner, along with the wiring differences.

  2. 2

    I’m replacing a Honeywell T8000C. When I was labelling the wires, the White wire was wrapped around both Y and W screws. I have a heat pump and would like to know where this White wire should go in my new thermostat which is Honeywell RTH6400D. Thanks for any help you can offer.

  3. 3

    Hi Shannon,
    My initial advice is what has been given in previous replies. See what electrical board terminals the wires connect to on your heating device.

  4. 4

    i have a red, Green, Black, yellow and orange wire I see where the red green and yellow go I am confused about the black and orange can you help?

  5. 5

    Hi Glen,
    See if Manuals Online has your old thermostat manual. Beyond that I always suggest to remove the blind guessing game equation from the process and locate the electrical board of the heating device you’re wanting to control and see which wires are connected to what terminals. Keep in mind a thermostat is just a controller that is sending low voltage(24v or less) signals. Ultimately the thermostat terminals need to be linked to the corresponding heating / cooling device terminals.

  6. 6

    I’m trying to replace an older Honeywell heat pump thermostat T874R1137 with a newer Honeywell WiFi TH9320WFV6007. The old has a ‘W’ white wire that the new one doesn’t, and the new one requires a ‘C’ wire not on the old one. Also, the old one has separate O and B wires yet the new one seems to combine these. How do I wire this? Honeywell’s web site doesn’t provide the manual for the older model.

  7. 7

    Hi Amanda,
    Most troubleshooting requires a hands on approach. There are several tests to perform that can’t be done over the phone or online. I would start by checking your furnace installation manual – check manualsonline if you don’t have a current manual – then recheck the wiring to the thermostat again. If all checks out I would then grab my low voltage detector and make sure I’m getting current. Unfortunately this may not be a common tool.

    The wires in the wall may match something you see in your furnace electrical panel, but that doesn’t mean they link together. There are only so many combinations of wire colors and they may be leading to something else. Maybe there was another heat source (e.g. electric baseboard heater) at some point. So the 2 wires you found tucked away may now lead to a dead end, a new 4 wire set was installed going to your existing furnace which does not include a 5th wire for common (24C). Hope this makes sense?

  8. 8

    We are replacing an old 4 wire thermostat with a new Honeywell 6580 5 wire. There were two wires pushed back into the wall. We made sure that all the wires match what is in our AC/Heat electrical box and the same wire match on the new thermostat. Our furnace panel is back on with the green light showing lit up, but still now power in the new thermostat? I’m assuming something to do with the C wire not having the current but no idea why?

  9. 9

    Hi Christy,
    Looking at the RTH221 Installation instructions, one of the designations states “a hot water system (steam or gravity) with or without pump — 2 wires”, so this thermostat should be compatible. There is only one way to connect and have the thermostat working properly. Were the original wires marked so you know what they originally connected to, or do you remember? I’ll need a basic starting point. If you only have 2 wires, did you remove the jumper between RH and RC? If so that needs to be put back in?

  10. 10

    we are trying to replace a two wire thermostat for steam base board heat with a honeywell rth221b. we have connected it several ways and still not working, did i buy wrong replacement thermostat?

  11. 11

    Hi Dave,
    You’re partially correct. But if you are referring to a neutral (commonly white wire) in your high voltage (110-120v) electrical system, that won’t work. The thermostat to furnace electrical panel are only low voltage components (24v or less). Am I understanding and answering your question appropriately?

  12. 12

    I want to replace a four wire thermostat with a five wire wifi thermostat. The fifth wire is the ‘C’, or common wire. Is this wire a ground / neutral wire to complete the power the display? If this is correct, I can connect the other end of ‘C’ to an electrical neutral and the thermostat will work. Right or wrong?

    Thanks very much for any information.


  13. 13

    Looking at the RTH6500WF instructions for heat pump use, it states “If old thermostat has separate wires on AUX and E, place both wires into the E/AUX terminal. If
    old thermostat has wire on AUX with a jumper to E, place wire on E/AUX terminal. No jumper is
    required.” You said you didn’t connect your old “E” wire to anything?

  14. 14

    I’m having an issue with my new thermostat not turning on my heat pump and only running my back up furnaces. I installed a Honeywell RTH6500WF. My old thermostat had a W2 and an E wire. I left the E wire unplugged based on what I read in the instructions saying both were not necessary. What have I done wrong? This is killing my electric bill.

  15. 15

    Hi Adam,
    With so many products and wiring variations, having a quick and simple answer isn’t always possible. Many times I find myself just having to analyze and figure things out, and eventually I do. If you have a solid understanding of wiring but maybe need original product manuals to help guide, I believe you’ll be able to sort out your project as well.

  16. 16

    i have 2 wire baseboard water heat but think wiring done on favor from a buddy for last home owner. my 2nd floor stopped working figured i would update old thermostat but it needs 3 wire to plug in to new honeywell. I work on cars for living but before pay someone to look at it like to know if its something simple that i am missing. Really don’t want to call anyone in just yet.

  17. 17
  18. 18

    I’m confused about the jumper on the R and Rc. I did not use the jumper, and the system seems to be operating ok. Do I need to put the jumper back on?

  19. 19

    Hi Chris,
    You can take the front panel off your furnace (first turn power off at the breaker or there should be a on/off switch near the furnace as well), there might also be a smaller interior panel, and access the furnace electrical panel where the thermostat wires connect. Use the diagrams in our article and the instructions for your thermostat to coordinate.

  20. 20

    Having replaced a couple of thermostats in the past, I didn’t realize the colors on the system I have now (new-to-me place) might not be following standards. They aren’t, and sadly I didn’t think to take a photo before removing the old thermostat. What suggestions do you have for figuring out what is what?

  21. 21

    Hi Tony,
    Being able to diagnosis so many combinations, especially without seeing the equipment on hand is near impossible to do. I believe we laid out the fundamentals and provided enough references so homeowners can then better understand their equipment manuals better and how to connect those components together. I can only suggest re-reading the wiring information provided and look at how your equipment is connected via those wires and I’m confident you’ll eventually get everything to work properly.

  22. 22

    Wanda, more information is needed? What thermostat terminals did the existing wires connect to? What type of system do you have, e.g. boiler…forced heat…etc?

  23. 23

    Thermostat has a white blue green red and Have new honneywell program. thermostat can’t get it wired up.

  24. 24

    Replaced a Honeywell t-stat T7300F2143 with a VENSTAR T1050 to control a trane HP package unit. The wiring to the honeywell t-stat was OB white,Y1 yellow,G black, R red, and X to brown. The connections to the T1050 is R red, G Black, Y1 yellow, BO W1 white, C brown. Although the green light on the T1050 comes on in cool mode I get heat instead of cooling. The other two modes Fan and Heat work.
    Is there anything you can advise me to do?
    Thank you

  25. 25

    Hi Ellen,
    With so many wiring variations, the best option is to compare the thermostat wiring directions with your heating and cooling device and then use this article guide and additional links for further assistance on terminal descriptions. If you don’t have the manual for your baseboard heater, you may find it at

  26. 26

    I’m replacing a real old Honeywell round thermostat for electric baseboard heat with a new programmable one (which has a lot of slots for different colored wires)… I only have 1 wire that comes out of the wall that splits in 2… 1 ribbed(neutral?) & 1 smooth(hot?)…which slots does which go into? B? W?

  27. 27

    Hi Tim,
    The furnace board and thermostat terminals that the existing wires connect to will tell the complete story. Color of the wires should be standardized but a previous installer could have used whatever color to connect “X” function. So, color alone doesn’t tell me what is connecting to what function.

  28. 28

    I am replacing an older thermostat with a Honeywell wifi programable one. My problem is the number and of wires the first old one has. I don’t want to miss something. My old one has six wires connected, a yellow, brown, green, white, red, and blue what goes where?

  29. 29
  30. 30

    I purchased a CT31A Honeywell non programable thermostat to replace a programable thermostat. The new CT31A has terminals for 4 wires red, white, yellow and green. The old programable one has 5 wires red, white, yellow, green and black. What do I do with the 5th wire?

  31. 31

    If you only have 4 existing thermostat wires then I don’t believe any of the newer digital thermostats can function as they are designed to have the 24v Common wire to complete their electronic circuit. This article provides much more depth on electrical wiring.

    You asked which Honeywell thermostats work with only 4 wires? I would contact Honeywell or look through each manual and see what their wiring requirements are. The manuals can be found in pdf form in each thermostats product page. eg.

  32. 32

    Hi, I have an older Honeywell that I would like to replace with a newer wifi programmable thermostat. I looked at the wiring that goes to the older Honeywell and I have the following:

    W1 – going to W1 connector
    W2 – going to W2 connector
    2 Red wires – both going to the Rh connector

    My question is what Honeywell product supports this setup?

  33. 33

    Hi Tim,
    Wiring in reverse will not be a problem. The 24C is required in some thermostats to complete the circuit path for their electrical design. But if your thermostat doesn’t require the 24C then there will be no harm leaving it unconnected. For future reference label this wire by the thermostat, cap it off with a wire nut so there are no electrical short issues, and just tuck it away where it can easily be accessed.

  34. 34

    Hi Denny
    First off, It’s been a year since the last question, I don’t know if you still answer questions but if you do….Thanks for providing a place for DIY’ers to get quality answers for their heating problems..

    I have a Lennox lp gas furnace with off peak electric and A/C. My current non-programmable thermostat uses 5 wires (the C 24v common wire), the new Honeywell programmable uses 4 wires (saying don’t hook up the C wire) Will this cause a problem?

  35. 35

    Hi Rodney,
    With so many thermostats on the market I don’t have any definitive troubleshooting knowledge of each one, especially when not seeing the products in person and having the ability to do a first hand inspection. If you did the wiring correctly and the blower motor for the AC is turning on, I’m not sure why the call for heat doesn’t work as well, the furnace blower motor is used for both operations. I can only suggest re-checking your wiring on both the thermostat and furnace electrical panel, and going through the settings again. There is always the possibility of a faulty product too.

    I suggest looking into Amazon or other reviews of your exact product, maybe someone else had a similar issue and solution.

  36. 36

    I just installed the RTH5100B with the 4 wires to correct terminals. The fan does not come in auto heat. It comes on with AC auto. It is a gas furnace with Ac. What could be the problem?I have tried all the different settings.

  37. 37

    First off, thermostat wires are all low voltage, meaning they are only signal wires sending 24v or less, so there is no risk of electrical shock. But if you have no electrical knowledge or experience you may be best off having someone that does survey what you have and what is needed for the upgrade.

    If you have an existing HVAC technician or think you will need one soon for a new furnace and/or air conditioner, you can contact an HVAC company as well, and have one of their techs do the upgrade, while hopefully building a reliable and solid relationship in the process.

  38. 38

    I have an older thermostat and am trying to assemble a programmable thermostat. The current one only has 2 wires connecting it and the programmable one had 3 spots for wires . I know nothing about electricity or wiring and wondering if I need an electrician to install this.

  39. 39

    Hi Tom,
    If you’ve already had a service tech on site that can perform tests and are dealing with the manufacturer, they are going to be better able to advise than us.

  40. 40

    We live a condo with 4 zones. It is a gas burner. The service man advised us our relay was bad. I sent away for a Belimo matching relay. Our Loft zone keeps calling for heat. I changed the relay correctly. While waiting for part I discounted the 3 wires from the unit and rotated counter clockwise for no heat.
    After installing new unit same problem occurred. I then disconnected all the wires to the thermostat and still the heat kept coming on. Not until I disconnected the3 wires from the Bilimo relay did the heat shut off.
    What is causing the heat to come on? Please help.
    The Belimo company said he was sending the same relay although the numbers may be different now.

  41. 41

    As straightforward and standardized as some things should be, advising without actually seeing what one is working with may lead to issues as there are variances between products. Following your manufacturers wiring instructions, take a look at your furnace electrical panel and connect the furnace terminal wires to the correct thermostat terminals. This article adds further explanation to thermostat wiring.

    From my understanding you have a 5 wire setup that requires you to remove the R and RC jumper.

  42. 42

    My old round Honeywell thermostat has a W terminal with a white wire, Y terminal/Yellow wire, G terminal/Green wire, R terminal/Red wire and an RH terminal/Blue wire. My new Honeywell RTH2300 programmable thermostat has W, Y, G, R, and RC terminals.

    Does the diagram above mean both the RH and R wires go on the R terminal, or should I tape off and abandon one of them or take the jumper between R and RC and put one of them on the RC terminal, and if so, which one?

  43. 43

    I found the best option for my needs with this same situation was to add a new set of 5 wire thermostat wiring. Read the section of our article on why the common wire is needed. For me this wasn’t an very difficult task as our basement ceiling is fully exposed and I could follow the existing wires to the furnace, then feed the new wires by taping to the existing wires and pulling up through the conduit to the thermostat wall opening. Not sure of your situation?

    The batteries you mention are just power failure backup to save the settings.

  44. 44

    changing out old thermostat have 4 wires w g y r no common had batteries trying to install new wifi programable dont need wifi what the wife bought what to do about no common

  45. 45

    Hi Mark,
    You mention a “T” furnace terminal. Lennox Furnace? If so, yes, the low voltage “T” terminal on the furnace can connect to your thermostat C (common terminal).

  46. 46

    Furnace has R, W, Y, G, and T terminals, but only R, W, Y, and G at the thermostat. Is the T terminal the same as the C (common) that I need for new programable thermostat? (I have ac unit too.)

  47. 47

    Hi Lori,
    Yellow is normally for air conditioning. Do you have an air conditioner? Best to go into your furnace and see what terminals the existing wires connect to. You can use any color wire as long as it connects the correct thermostat and furnace board terminals.

  48. 48

    I have a green, red, white and blue wire from my old thermostat. All of the programmable directions require a yellow wire. Is one of the wires interchangeable with the yellow wire?

  49. 49

    Hi Bobby,
    There is no timetable on replacing your thermostat from my knowledge. Just replace when the unit goes bad.

    If your current thermostat is old enough that it contains mercury, please contact your local waste disposer for proper disposal.

    If you are in the market for a new thermostat, please view our Thermostat Buying Guide.

  50. 50

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