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Honeywell Thermostat Wiring Instructions

When 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, and if you need to budget for an electrician or hvac tech to install the proper wiring.

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.



Leave a Reply
    • Hi Scott,
      We are a blog that tries to fill in some of the blanks but don’t offer any one-on-one services beyond the comment section. If you require direct service for a Honeywell product, please contact their customer service, or contact a local HVAC tech or electrician that may be more familiar with your exact make and model of thermostat.

  1. I’m replacing a White-Rodgers thermostat with Honeywell RTH7500D. My AC wiring consists of G, W, RC, RH (a piece of removable wire that was connected to the RH and the RC), and 2 Yellow wires that were connected on the same terminal. Question 1: Where should I connect the yellow wires? Question 2: What do I do with the piece of RH wire? Thanks for your assistance.

    • Update: I only had 1 Yellow wire. The other yellow wire was connected to the old thermostat. I was able to connect the new thermostat and it is running nicely. However, my lights are flickering. Question: What is the RH wire for, and do I need to connect it? Thanks again.

      • One last thing: The A/C is not cooling like it should. What do you think is causing it?

      • I am having the same issue with the A/C not cooling like it should. Would also love an answer to that problem.

      • Hi Chris. I did call Honeywell and they helped me to program my AC. Did you program it? Now, mine is still not cooling so I had to call my AC tech. I wish you well.

      • Chris, the tech just left. He said that the AC capacitor had gone out. I asked him what is the capacitor. He said that it turns the compressor on. That’s why my lights were flickering because it was trying to kickstart it but it wouldn’t budge. So try that. I hope it helps. He did tell me that I did a good job installing my own thermostat because it’s a tricky one. I praise God that it all worked out. It’s cooling nicely now!! He charged me $200. Be blessed.

      • This is a great example of how not everything can be solved on the internet. Many issues need a hands on approach by an experiences technician. Glad you’re up and running smoothly now Tracie. We appreciate your responses and willingness to help others that may come across similar problems.

      • Denny, you’re welcome. Thank you!! Yes. You are correct about seeking an experienced technician. However, many times we seek the internet as a means to save money and not to be forced to call someone for everything. As being single, that’s why I attempt to do things myself, because I will never have any money if I have to constantly call someone for everything that happens in my home. Like I told the AC tech today, if you can read and follow directions, then you can pretty much do anything. In saying that, I’m not a fool. I’m not going to really attempt something that I have no knowledge with like going outside and changing an AC capacitor. LOL. I know my limitations. Thanks for the comment!!

      • I have another update and hopefully this will be the last one. I had to call the AC tech again Saturday because my unit had stopped cooling. He thought it could probably be the blower and then told me that I must have done something wrong with wiring the thermostat. He asked me where I put the G wire, etc. Now, grant it, it was working when he replaced the outside capacitor. Anyway, I texted him a picture of the model and serial numbers so he can pick up the parts before coming to the house. So he told me that it was the capacitor. He said the unit has an outside and inside capacitor and that lightning could have hit it. So, the house is cooling again. Thank God!! I did tell him that he hurt my feelings for saying that I didn’t install the thermostat correctly. He laughed and said, “No. You did do a good job and that most women wouldn’t do it or let alone touch it.” LOL. I hope this helps you all. Be blessed!!

      • Oh, he only charged me $35, the price of the part since he charged me labor on Friday. Praise Jesus!!

      • After waiting a couple days to confirm that this will be my last comment, I can now tell you that I had to call the AC tech out again because the unit kept freezing up on the inside although the outside pipe was showing frost on it; however, the unit was still on outside but not inside. After I would let it thaw for a couple of hours, when I turned the system on it would make a stirring sound but wouldn’t start, I would then flip the main AC switch on the unit to the off position (not on thermostat), wait a few seconds and flip it on; the unit would start. The AC tech checked the blower and said everything looked good and didn’t know what it could be. When I told him what I had to do to start the unit, he said that it could be the relay switch to the unit. He changed it for free and called me later that evening to see if it was working. It’s been a couple of days since then and everything is working perfectly. Thank God!! He did tell me that the capacitor still had to be changed because the unit was working outside. I hope this helps someone. Be blessed.

  2. I did this wiring exactly… but when my cool on stops flashing, my fan doesn’t come on in the inside or outside… it was working just fine before… and i replaced it exactly. #confused

    • Hi Fran,
      I’m not sure what thermostat you’re referring too? The ones given in the article are just random examples to show the differences between 4 and 5 wire models.

      Trace your wires back to the furnace electrical panel and triple check that all are making the appropriate connections.

  3. I’m going from an old honeywell analog thermostat to a new digital programmable one. My unit is a heat pump. I have figured out what all but a few wires are going to. The ones im most concerned about are W1 and W2. The connections I have on the new terminal are K,L,Aux/E, G, O/B, C, Y, R, RC. I know W2 is supposed to be my 2nd stage heating and should goto Aux, but where should I put W1? Does it goto the Aux terminal as well? Wouldn’t that cause Emergency heat to run all the time?

    Also on my current thermostat the Yellow and Green wires are both on the G Terminal. Shouldn’t the compressor be on Y terminal?

    The connections for my current (old) thermostat are :
    Terminal/Wire Color
    X-Blue (Common on the unit)
    L- No wire
    W2- White
    R- Red
    G- Green and Yellow
    O- Orange
    Y-No wire
    W1- Brown
    E- No wire
    B- No wire

    Thanks for any help

    • Hi Charles,
      Giving exact advice over the internet about a subject that involves so many different devices is difficult. From my experience, thermostat installation instructions provide both furnace and heat pump wiring guidance. If you are in need of installation instructions for your heat pump as well, try these two sites (manualsonline or manualslib). Together, you should be able to sync the two.

  4. I’m interested in buy the Honeywell RET97E5D1005/U Wi-Fi Programmable Thermostat and I’m trying to figure out if I have a C wire. I’ve done a lot of research but I can’t seem to find the answer in my particular situation so I’m going to do my best to explain it.

    In my thermostat I currently have wire connected to G, Y, W, and RH. And I also have a jumper going from RH to C (this is the part that’s throwing me off). I have a volt meter and I tested the voltage on all the connections. While touching the RH/C connection and any other connection I got around 28 volts with the air system running and not running. If I tried any other connection that didn’t included RH/C then I would not get any volts while the system wasn’t running.

    In my indoor ac unit my wires that run to my thermostat are labeled C (runs to RH/C), Y (which runs to Y), W1 (which actually runs to G), and a no labeled wire that runs to W. I can’t be certain but it seems that the labeling might be incorrect and that it’s actually suppose to output as R, C, G, and W, but I’m going to continue to refer to the wires as I stated them originally. I traced the C wire back into the unit and discover that it comes directly from the transformer right after it is transformer from 220v. Furthermore if I follow the C wire the other direction (towards the thermostat) then it runs down below the air filter and connects at the frame of the unit to a device that is wrapped in tin foil. The wire runs into the device and then come right back out and runs to the thermostat and is plugged into the RH/C connection.

    That Is all the information I have gathered. I am determined to figure this out and would love some guidence that anyone could offer me.



    • Hi Logan,
      You started off stating that you have a 4-wire setup (G,Y,W, and RH). With this I am going to say you need to run an new set of 5-wire so you have the common needed for your new thermostat.

      Did you click over to the link In-Depth Thermostat Wiring Explained. I believe the information will fill in the gaps of knowledge you’re looking for.

      Your second paragraph mentions an indoor AC unit. Is this running on the same thermostat or separate?

  5. 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.

    • 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.

  6. 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?

    • 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.

  7. 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.

    • 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.

  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?

    • 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?

  9. 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?

    • 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. 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.


    • 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?

  11. 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.

    • Hi,
      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?

  12. 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.

    • 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.

  13. 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?

  14. 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?

    • 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.

    • 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?

  15. 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

    • 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.

  16. 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?

    • 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

  17. 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?

    • 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.

  18. 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?

  19. 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?

  20. 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?

    • 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.

  21. 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.

    • 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.

  22. 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.

    • 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.

  23. 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.

    • 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.

  24. 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?

    • Hi,
      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.

  25. 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

    • 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.

  26. 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.)

    • 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).

  27. 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?

    • 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.

  28. 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.

  29. Hi Oscar,
    Per the instructions in the article, you’ll need to buy a new set of 5 thermostat wire. You can always just add a single wire for common too, but since you’re needing to pull wires anyways, mine as well get a new set that is grouped together. If you don’t feel comfortable doing this, then you can call an electrician or HVAC tech. Sorry, there is no easy alternative. The thermostat can’t fully communicate with your furnace without the common wire.

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