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Questions tagged [thermostat-c-wire]

The "C" or Common wire provides a way to get constant 24VAC power to the thermostat, now required by many newer thermostats with WiFi and/or touchscreens.

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Connecting Wood/Electric Furnace to Smart Thermostat

UPDATE: I spoke with an ecobee tech and they pointed me to an alternative solution. If I get an adapter called a "Fast-Stat Common Maker", all I need to do is figure out where to connect the C-Wire ...
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Ecobee 3 lite Installation — Confusion about C wire (on furnace but not at thuermostat)

I am about to install the ecobee 3 lite thermostat. On the thermostat end, there is no C wire - just the typical 4 wires - R,Y,W,... On the furnace end though, there is white C wire too, which I do ...
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smartzone or Furnace: c-wire to smart Thermostat

I'm about to add the c-wire to smart Thermostats. However, I'm not sure where to connect it as I have the following options: I have two zones, ( and I have two smart Thermostat) , I can connect the c-...
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Need to identify a common wire on my old HVAC

For Nest Thermostat 3, I am trying to identify a common wire on my old HVAC. The diagram can be found on the link below:
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828 views

Where do I connect a C wire in an old Furnace?

I am hoping to be able to upgrade to a smart thermostat but unfortunately my furnace doesn't have the "easy" option with an obvious C terminal. My furnace is OLD but it actually has the full 5 ...
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Connect Wifi Thermostat to Goodman GMP050-3?

I'm trying to connect up a wifi thermostat to Goodman furnace, specifically the GMP050-3. I've done some reading on this but I'm still not quite sure how to go about it. Specifically, I'm not sure ...
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Gas Furnace only, is Y wire needed?

I have force air (propane furnace). I would like to upgrade to a new "smart" thermostat, but they didn't run a C (common) wire which is required for most of these units to run properly. I do however,...
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Which terminal should I connect it to for a “C” wire on an american standard AM4A0A30

I'm trying to connect a 3rd gen Nest thermostat. I have a 2 zoned heat and 1 zone AC. The zone with this thermostat has a boiler wired Rw, W1 and HVAC wired Rc, G, Y1. It's summer so I'm only using ...
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How to identify the C terminal on my HVAC [duplicate]

As you can see I have a Y G W R/2 C/3 D/1 terminals on my HVAC. I am planning to change my thermostat to one that requires a c line. There are 2 spare lines available, however I am not sure which is ...
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708 views

Is the transformer bad on my Central Air Conditioner?

Need some help diagnosing a problem. My very old central AC unit isn't working. It's just AC and about a year ago I connected a C-Wire to the air handler when swapping the thermostat for a wifi ...
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Nest thermostat to Kelvinator furnace

My old thermostat had 4 wires. I replaced with a Nest thermostat. At times the AC condenser is running but the furnace blower is not running. Found other with this and they said need to add common ...
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Just another C wire problem

Sorry for the long post but if you can make it to the end, I would greatly appreciate it. I have what I believe to be an uncommon situation that I haven't been able to solve. I have a thermostat that ...
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36 views

Wifi thermostat

Can I connect C-wire to the empty terminal(red arrow)
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440 views

Where to connect c wire in furnace?

I'm trying to figure out where to connect a C wire from a thermostat to my furnace. I found this old post for the same furnace type (Trane XE70), but it seems as though a red wire goes to the terminal ...
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Why does my Nest thermostat report error e195 when I try to use the air conditioning?

I had a Nest E installed in February and it has worked really well until it was time to turn on the AC. Now I get random e195 errors (no power detected to the R wire). The most likely answer from my ...
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Thermostat Replacement - what to do with C Wire

I'm replacing an old Honeywell T8195B with a less old Honeywell T8112D1005. The T8195B has the same wires as the T8112D1005 - except the T8195B also has a C Wire. The C Wire location on the ...
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247 views

Adding Unused C-Wire for Nest Thermostat

I'm having an issue with my NEST thermostat short cycling my air handler fan while in running AC. This is a known issue, and the fix seems to be adding a common wire to the NEST. My thermostat is ...
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691 views

Where should I connect a C wire on my Goodman PGB030075-1 furnace?

Is this where I can piggyback for c wire on Vine thermostat? Thanks
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182 views

Adding C wire to WiFi thermostat

I’m trying to add c wire to furnace to run a WiFi thermostat but don’t know where to hook up c wire to get power to turn on thermostat i have 2 extra wires just don’t know where to put one them to get ...
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C wire problem for WiFi thermostat [duplicate]

I’m trying to add c wire to furnace to run a WiFi thermostat but don’t know where to hook up c wire to get power to turn on thermostati have 2 extra wires just don’t know where to put one them to get ...
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1k views

Can a Ground Wire be attatched to a nail in wood stud?

Guilty as assumed: I've installed a thermostat connected to a single electric baseboard. Is it possible to connect the load and line ground wires to a nail which is attached to a wood stud? OR, simply ...
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232 views

What are these extra wires behind my thermostat?

I an hoping to install a new thermostat that requires a C wire. I pulled off my old thermostat, an old round dial type, and it was of course only connected to four wires. The four wires are the only ...
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2k views

Nest, Blue Wire, W1 and W2

I just got a Nest E thermostat and I'm trying to hook it up. There is a blue wire that I had assumed was the "C" wire, but looking at the furnace, it doesn't look like that's the case, as the blue ...
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141 views

Connect C wire to Carrier board

I got Carrier board HK61EA010 and extra C-blue wire that is not connected to the board. I wanna use this wire to power WI-FI thermostat. I cannot find the manual for this board. Does anyone know where ...
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1k views

Where to connect my “c” wire on the boiler side. Weil mclain gas boiler

Im just curious if the “c” terminal on the plug in relay is where im suppose to connect my “c” wire on the boiler side. I have 18/5 wire ran already. Just need to find out where to terminate. To the ...
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3k views

No C (Common) terminal on Furnace.

I am trying to hook up a new wi-fi thermostat. I currently have 4 wires running, but there are many unsued that are terminated in the jacket of the wire. No issues there. However, when I ...
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767 views

Wiring a new thermostat without a C wire, extra wires from furnace

I have checked other posts regarding this and don't see a solution yet. I have purchased a new thermostat that requires a c wire. My old thermostat's c wire didn't work so I went ahead and added a ...
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2answers
228 views

Nest E Thermostat Power

My thermostat is in the basement, connected to a Honeywell R845A to run a circulating pump for heat. I bought an Nest E for the main house and it works great. I want to replace the thermostat in the ...
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1answer
276 views

Installing a smart thermometer (ecobee4) can I move the wires around on the HVAC?

I want to install an ecobee4. I want to install it with the C wire so I do not need to use their kit. It seems to me that I should be able to just move the wires around on my hvac. Here is a diagram ...
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2k views

How to wire C wire to the transformer of HVAC?

How are you all doing? I tried to connect the digital thermostat (Ecobee3) instead of my old honeywell thermostat. The original wiring is below (figure 1) HVAC is located on the ceiling of bathroom ...
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59 views

Want to add Wifi thermostat to a 20yr old Coleman Furnace

I have a Coleman furnace model number 7966A 856... Its a 2 wire heat only system ...No circuit board! I tried to add a photo but could not do to size restrictions. One red wire one white ...and two ...
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924 views

Add-A-Wire - COMMON / C Wire to a 3 Wire Thermostat

I am battling a Nest and losing at every turn. I have a 2 zone system and was able to install a Nest on the 1st floor by repurposing a wire as a COMMON wire. Unfortunately, the 2nd floor only has 3 ...
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Home thermostat woes

I tried to switch to a new smart thermostat in my home. When I was adding it, something happened. The new thermostat didn't show any power (And yes, the C wire was plugged in). Not knowing what else ...
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How can I install a Honeywell Wifi RTH6580WF1001 thermostat in place of a Honeywell RTH2300b?

I have separate heating (hot water) and air handler (cooling System). The current thermostat I'm using is a Honeywell RTH2300B and the new one I want to install is a Honeywell Wifi RTH6580WF1001. The ...
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Confirming C wire in my thermostat

can someone confirm that the blue wire is the "C wire"? What are the other wires (yellow, light pink, brown, and orange) that are not connected to anything?
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577 views

Wiring C-wire in old Rheem

looking for some help with an old Rheem 1005 HVAC system. I’ve scoured the Internet for days, so this is a last ditch effort at self-help. I’m installing an ecobee to an existing 4-wire system that ...
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722 views

Need Help on Adding a Common Wire for Nest

I recently purchased a Nest thermostat. After couple weeks of usage, the Nest is constantly shut down due to low battery. I search online that adding a common wire is the go solution for this. However,...
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can I use an unused y2 or w2 aux wire and connect to the C terminal

I got a new ecobee thermostat that requires a c wire. my current thermostat has 4 wires plugged in, and there are 2 extra wires not being used coming out of the wall one blue labled y2, and a brown ...
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139 views

Adding a C wire to older 3 wire

How do I use the green wire as a C wire as suggested in most installation instructions for the newer wi-fi thermostats? They all reference terminal strips at the furnace, all I have is the 3 wire ...
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842 views

Can I use the Y wire in place of the C wire for my new thermostat?

I'm looking to wire a Honeywell Lyric T5 to my furnace (I do not have an air conditioner, I do have a humidistat). My current wiring at the thermostat is G,W,Y,R. At the furnace it's G,R,C, and 2 at W,...
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Why doesn't my thermostat work?

I replaced old thermostat with Honeywell wifi and added C wire from furnace to new thermostat. I left the jumper wire on Rc and R in place and wifi would not come on line. Checked C wire and have ...
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116 views

Can I use the extra thermostat cable as C cable for wifi?

I just purchased an ecobee4 and I found that I need C wire for wifi which is not connected to my current thermostat. However, there 2 extra wires I found in the wall. Could you use one of them for the ...
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1k views

How do I connect the spare C wire to the old Lennox system (model # lennox g12q4-110)?

I am trying to install my Ecobee3 now. After finishing the connections, Ecobee did not power up. I did some reading and I believe the C-wire, though it is available is not connected to the power at ...
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1answer
11k views

Nest thermostat not turning on heat

I have an old gas furnace/boiler for hot water baseboard heat and I'm trying to switch from a 2 wire mercury bulb thermostat to a Nest Thermostat "E" (the new white faced one). There are 5 wires in ...
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182 views

Where to connect c wire

I’m installing a new WiFi thermostat that needs the c wire. I ended up running new thermostat wires that contained the common wire but now I’m stuck on where to connect it to the furnace. Can ...
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428 views

C Wire for Thermostat

I am upgrading my thermostat (Have AC & Heat) and found that it doesn't have the "C" wire that I need to power my new thermostat. The furnace does have a terminal for C, but only condensation pump ...
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2k views

How do i hook up a new 5 wire cable to an existing 4 wire furnace

I would like to replace the existing thermostat wires on my 2000's era janitorial furnace with the upgraded 5 wire setup that will allow fan control of my Honeywell wifi 9000 thermostat. I was going ...
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294 views

Can I add a “C-Wire” to boiler with this device?

https://www.amazon.com/FAST-STAT-Common-Thermostat-Extender-Connection/dp/B01N6ERM04/ref=pd_sim_60_4?_encoding=UTF8&psc=1&refRID=D3D121DG0B4379V2TRC6 On the surface it appears that it will ...
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158 views

How to connect wifi thermostat with a boiler after cable upgrade?

I have an old battery operated thermostat right now with two wires (18/2) attached to it running to a boiler. No AC, fan, etc.-- just a boiler. I can easily replace the wire with 18/5 one, however I'm ...
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218 views

WiFi Thermostat - C Wire

I am trying to install an Ecobee 3 thermostat to replace the upstairs one I have now but the 3rd wire isn't connected to anything on either end. I added the basement thermostat just to complete the ...