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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62 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
34 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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47 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
86 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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336 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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592 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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203 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
710 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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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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32 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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708 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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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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327 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
89 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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960 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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76 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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179 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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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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1answer
662 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
422 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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975 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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254 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
43 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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125 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
190 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
593 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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55 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
73 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
101 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
61 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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41 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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27k 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
70 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
69 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 ...
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1answer
51 views

Where do I put the C wire in this setup

Got me a wefe thermostat. Old thermostat used 4 wires but the blue C was stuffed in the wall. I have read many forums and nobodys setup really matches mine. This what I see at the furnace and what I ...
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1answer
50 views

Where to install C wire?

I need to run new thermostat wire since I don't have a C wire to power my smart thermostat, but need some guidance on where to hook it up. I have five wires at my thermostat, two going back to my ...
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2answers
209 views

Lennox G23Q3/4-100-2 And Ecobee4

**Pictures attached to go along with my rambling explanation I have my Lennox G23Q3/4-100-2 natural gas furnace and my central air system that has been working since 1995 on a basic programmable ...
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1answer
302 views

C wire - thermostat - not providing power

I'm replacing my old Honeywell thermostat with a new Wifi thermostat. My old/current one is battery powered and doesn't use the C wire. I found the C wire behind the plate. I connected the c wire to ...
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44 views

Thermostat wire does not go to Furnace

My thermostat wires go to a control panel heat pump system which go to the furnance , i need to wire a c wire but not sure how to go about this with the york control panel
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1answer
101 views

Can't get wifi thermostat to work with gas boiler

I bought a Sensi WiFi thermostat and I have been trying to install it. I can't quite figure out how this wiring should work. Here is a link to pictures of the boiler and the current thermostat. The ...
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36 views

Identifying C wire

thank you in advance. I have been struggling to find a proper way to install my ecobee. It is again 'C wire' issue. My old thermostat uses 4 wires (red, yellow, green, white) and does not use c wire. ...
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1answer
48 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
27 views

How do I determine where to connect a new C wire inside my furnace when no control panel or wiring terminal exists?

I am replacing my existing thermostat with a new smart thermostat that requires a C wire connection and the old unit did not. I intended to utilize the unused Blue wire which is not connected on ...
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1answer
34 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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41 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
63 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
679 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
776 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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2answers
89 views

I have an unused C wire hooked up to thermostat and have no idea where to connect it to the furnace for power

I know this question gets asked all the time but I've spent hours staring at forums as well as my furnace and at this point I'm desperate. I just bought a nest thermostat that needs a C wire ...