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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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1answer
17 views

Where do I connect C-wire to Burnham boiler?

I'm adding a smart thermostat to one zone of a two wire, oil fired boiler system. I've roughed in a new wire and could use some help determining where to terminate it at the boiler. The wiring is far ...
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2answers
94k views

How do I identify the C terminal on my HVAC?

How do I identify the C terminal on an HVAC, furnace, or boiler? If the terminals don't have a screw labeled C what should I look for on the wiring diagram? What steps should I take if a wiring ...
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1answer
28 views

Need help with weird (?) wiring to thermostat and condensate pump

I've searched a lot and can't quite find what how to solve this one. I installed an ecobee smart thermostat, which didn't work with 5 wire connection so I switched to their PEK module with only 4 ...
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2answers
48 views

How do you install a thermostat if you don't have Y or C wires?

My thermostat is a LuxPro LUX PSP511LCa. I looked behind the thermostat and I see the following: A red wire connected to RC A jumper connecting RH and RC A white wire connected to W A green wire ...
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1answer
59 views

how to connect C wire for ecobee lite to Weil-McLain EG Series-5 gas steam boiler

I want to upgrade from a battery powered Honeywell thermostat to an ecobee3 lite. This is for heat only. My current Honeywell has two wires: Red and White. Missing is the C cable. There are enough ...
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1answer
36 views

Adding a C wire and fixing White vs Red on my Furnace

TLDR: I think I need to flip R and W wires, and to splice the blue (C) wire to the brown wire coming of the transformer. Is this correct? Long version: Like many others on here, I'm trying to add a ...
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3answers
2k 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
32 views

Secondary C Terminal on Furnace Circuit Board?

I was trying to install an Ecobee thermostat, and there was no C wire installed. When I went to install the power extender kit, I saw the standard C wire terminal was broken out of the black plastic ...
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1answer
36 views

C wire in wireless Thermostat Transofrmer question

I have a rheem handler with a 46-23115-02 transformer. I do not have a C-wire connection that I can see. I have a 5 wire cable... so I do have a blue wire available that I can connect as the common ...
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1answer
42 views

Where should I connect my C-wire on my old Goodman unit (GMP075-4 rev 13)

I want see if someone help me on hooking up this new Honeywell thermostat with Wifi I just purchased. I have an old ac unit and I only have 3 connections to my circuit board which does not have an ...
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3answers
68 views

Where to add a c-wire on my Goodman furnace?

I'm looking to upgrade my old thermostat and need to run a c-wire. Where would be the best place to tap into?
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1answer
48 views

Furnace with no “C” connection

I have a mobile home furnace. This furnace only has a 4 wire connection terminal, G,W,R,Y. I also have a condensing unit outside with the 24 volt 2 wires coming to the furnace. I know I connect one to ...
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1answer
66 views

How to connect a new C wire

I have a 2 zone, single stage, heat only system with 2 wires running to each thermostat. I'm looking to install 2 Ecobee's; I have a second Honeywell AT72D1683 that I can install if needed and have ...
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1answer
2k 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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1answer
692 views

Need help adding a C wire for a wifi thermostat

With the increasing popularity of wifi thermostats I know this question has been asked many times, however I'll ask it again fr my specific situation. How do I add a "C" wire to my existing air ...
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1answer
798 views

Want to add a WIFI thermostat, but no 'C' wire… only 2 wires to each thermo

i have a 5 zone radiant floor, oil fired heating system. Each thermostat only has 2 wires running to it. i have a TACO SR506 switching relay that receives the wires from each thermostat and controls ...
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1answer
64 views

“C” wire on thermostat

I have an electric furnace that has power, fan, electric heat, but I do not have a "C" wire. The thermostat wiring has several unused wires that are routed to furnace. It is a matter of applying ...
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2answers
37 views

Replace thermostat wiring from my Carrier Weathermaker 8000 to my Nest thermostat

I'd like to replace the wiring from my Carrier Weathermaker 8000 to my thermostat to add a C wire. I assume I need to turn off the Carrier first, but there is no power switch that I can see on the ...
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1answer
51 views

C Wire in Air Handler

Can someone please help me find where to connect a C wire for my smart thermostat? Here are some pictures with descriptions. It is difficult to get to the 24v connection in the back. My schematic ...
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1answer
99 views

Smart Thermostat without C on Heater

I want to hook up my Honeywell rth9580wf to a natural gas garage heater that only has R, W, and G (not in use). It's currently hooked up to a standard battery powered Honeywell thermostat. I've read ...
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1answer
345 views

Connect C wire Lennox G16

I bought a new thermostat that needs the c wire. Old thermostat wasnt using the blue c and was stuffed back in the wall. Come to find out the blue c wire is not connected to the furnace. Trying to ...
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1answer
615 views

Wiring a C (common) wire to a Triangle Tube Prestige Excellence 110?

Wiring noob here. Can someone give me step-by-step instructions for where and how I should attach a C (common) wire to a Triangle Tube Prestige Excellence 110 boiler for a ecobee3 thermostat? I think ...
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1answer
218 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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1answer
756 views

Honeywell VR8300A3500 Single Stage Heat Gas Valve to Ecobee3 with C wire

Hey everyone have a quick question regarding a honeywell VR8300A3500 Single Stage Heat Gas Valve and the introduction of a Ecobee3 wifi enabled thermostat with a "C" wire. just want to make sure i am ...
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0answers
51 views

Replacing old thermostat and two unidentified wires

I'm replacing an old thermostat from the early 90's with a new wifi thermostat. When removing the old one, it only used R,G,Y,W wires, and the new wifi thermostat requires a C. After fully removing ...
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0answers
48 views

Only getting 15-16 volts from Furnace R and C

I recently purchased a smart thermostat. Because it needed a common wire and I only had a 3 wire setup, I ran a new thermostat wire to my furnace. However, I now get only 15 volts (inconsistently, ...
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1answer
737 views

Thermostat wiring with external transformer

So I am trying to wire a Honeywell lyric thermostat and I tried following videos but got a little stuck. So I have wires R, W ,Y , G coming to my original thermostat. I bought an 24V external ...
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2answers
10k views

Can't get the AC compressor to turn on after switching to Lyric T5 Thermostat

I swapped out my old thermostat with a Lyric T5 around Christmas time. I live in an older house so wasn't sure I could make it work. I opened my old thermostat and saw that there was a blue wire ...
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1answer
395 views

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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1answer
91 views

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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1answer
975 views

C wire and smart thermostat (with pictures)

I'd like to install an ecobee3 thermostat, but I'm not entirely sure about my wiring. The current thermostat seems to only have a W and RC wire coming into it. There is also what appears to be a blue ...
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2answers
78 views

Need a common wire

So, I recently moved. In my old place, I used my Nest without a common wire and never had an issue. However, in my new place, my Nest thermostat was working fine for about 20 days and started losing ...
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1answer
190 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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1answer
3k 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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1answer
696 views

Can I run a C wire from Fan Relay

We've just moved into a new home with an heat only, oil, forced hot air furnace. The current thermostats are very old and we'd like to update them to something like a nest. The furnace is currently ...
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1answer
442 views

Old AC and Gas Boiler wiring for new thermostat

I need help connecting a new 'C' wire for a Honeywell RTH6500WF thermostat. As you can see the heating is an old boilder with a simple pump to circulate the hot water to the baseboard radiators. The ...
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1answer
976 views

How can I add a C-wire to a Venstar T5800 thermostat?

I am trying to replace my existing thermostat. My old thermostat has: Rh, W (coming from the heating unit). Rc, Y, G (coming from the AC unit). On the Venstar T5800, I can map as follows: Rh+Rc -...
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1answer
258 views

C Wire placement in HVAC?

I'm installing a new thermostat and the previous one did not have a C wire connected. Tracing in back to the HVAC, I can't see a C output connection? Based on the wiring diagram (and reading other ...
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1answer
51 views

Where does my C wire go in this splice connection?

I'm looking to install the Ecobee3 Lite thermostat. My current thermostat has a blue C wire running to it, so my understanding is the PEK doesn't help because that is used if you have no C wire. On ...
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1answer
148 views

Thermostat C Wire (Possibly Unconnected)

I purchased a Honeywell RTH6500 Wifi Thermostat, which requires a C wire. My old thermostat showed a connected blue C wire. However, it was battery-powered. If I removed the battery, the thermostat ...
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1answer
204 views

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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1answer
598 views

How can I implement an unused wire as a C wire for my thermostat?

I have a boiler system that uses 2 wires to the thermostat. I am going to buy a new thermostat that needs a C wire. There is a spare wire not being used and it is not hooked up to anything. How can I ...
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1answer
58 views

Another “How do I add ”c" wire to boiler for Nest

I have tried searching this forum and others, but I could not find anyone with a situation like mine. I thought it better to ask here, rather than damage something. I have a Lennox wall mounted ...
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4answers
99 views

Wifi Thermostat, No C wire on HVAC unit. No control board? Condo

Looking to install Ecobee thermostat. Only 4 wires coming from unit. Ecoboo has power extender kit but there's no control board on the HVAC unit, so I can't locate a c wire. Any help would be ...
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1answer
109 views

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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1answer
62 views

Connecting Common Wire to Control Board

I have a heat pump and want to add a thermostat that requires a common wire. I have read through many threads that show how to add a wire but I already have a few extra in the bundle so its not so ...
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1answer
45 views

Is the PY4G HVAC unit compatible with Nest Thermostat?

I recently bought a Nest Thermostat and I've had nothing but trouble with it. The main symptom is the fan and the AC compressor won't run at the same time. Power only comes through the green wire, not ...
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1answer
28k views

How many wires can be connected to the C terminal at the furnace?

I'd like install a new Wi-Fi thermostat. The old one didn't have a C-wire but luckily there is an unused wire on both sides (one coming out of the wall and one at the furnace not connected yet), so I ...
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2answers
77 views

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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2answers
80 views

Can I pull a common wire off an evaporative cooler transformer relay?

I have a Nest thermostat currently controlling a LP furnace. The old thermostat didn't have a common wire connected, but there was a an extra wire in the bundle and a common terminal on the furnace ...