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
127 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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1answer
153 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
70 views

Where to connect C Wire to1990 Weil Mclain Steam Boiler

I am attempting to run a new 18/5 line in order to hook up an Ecobee 4 to my Weil Mclain boiler, as my current thermostat only has a R & W wire. I am having trouble figuring out where exactly to ...
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1answer
73 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
64 views

Installing a Nest thermostat without a C wire?

I am attempting to install a nest but do not have a common wire on my hvac unit, perhaps it is slightly dated. I have read that on older units the O terminal is the same as C and I can remove the ...
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1answer
62 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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1answer
35 views

Splitting Wires for Thermostats

A friend of mine wants to upgrade his thermostats to WiFi thermostats but the thermostat wires ran to the thermostats are missing the C wire. There are 2 thermostat lines ran from 2 units to 2 ...
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2answers
252 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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52 views

Old Steam Furnace

I have a old steam furnace that is running fine now but it’s not hooked up to the switch or the transformer. I have a brown wire (cable with brown insulation) containing a red and a white wire coming ...
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1answer
756 views

How to connect c-wire to Burnham Series 2 boiler?

I am trying to install my ecobee 3 light but the previous thermostat did not use any c wire. Fortunately, there was an unused wire in the wall and I would like to set it up as a c-wire. The problem is ...
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1answer
34 views

Where do I put my c wire the un used or c wire for me is blue but where do I connect it to?

I’m not really sure where to tie this blue wire into for my thermostat (https://i.stack.imgur.com/IJoRS.jpg)
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1answer
122 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
209 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
26 views

Nest thermostat e heat link replacing the old danfoss

I really need help with replacing this current danfoss thermostat with a new nest thermostat e heat hub. I'm in the UK. Below is the new heatlink just need to know what wires I need to wire and what ...
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1answer
1k 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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1answer
200 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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1answer
45 views

Checking my understanding - How to add C-wires for smart thermostat install x3

I'm in the process of installing some smart thermostats (Nest Thermostat E) to replace my old ones. I have a boiler radiator heating system with three zones. Two zones are straightforward heat only (...
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1answer
3k 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
119 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
2k views

Add a c-wire to 25+ year old Rheem furnace

I've looked at just about every post on adding a C-wire to power a WiFi thermostat but remain uncertain on how to proceed. The current installation on a Rheem RGAC-080A is two wire as here: XFMR - ...
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0answers
37 views

C-Wire for a Vulcan Gas Central Heater for Nest Thermostat-E

I'm hoping the friendly people here could help me. I'm looking to purchase a Nest Thermostat-E but my current thermostat (Vulcan/Bonaire Summer Breeze) only has 2 black wires connected. I've searched ...
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5answers
15k views

I am installing a Honeywell RTH6580WF with a TACO SR504

The current installation does not have a C wire. So I have run an extra wire and am now confused as to where to connect it. There is a 24VAC connection and a common connection. Comments say that ...
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1answer
38 views

No C terminal on furnace. Workarounds? Possible the AC?

I'm Trying to connect my C wire to install a new thermostat but the furnace doesn't have a C terminal. In my readings on this I found that because I have an AC,I can connect my C to one of the wires ...
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1answer
58 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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2answers
7k views

Wifi Thermostat to Reznor Garage Heater. No “C” wire connection on terminal strip

I just had a 75000 btu Reznor UDAP garage heater installed. Can I run a "C" wire for a smart thermostat if I don't have a C connection on the terminal strip? There is a C connection on the circuit ...
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1answer
63 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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0answers
21 views

Wiring c wire to current valve controller

I am looking to hook up a wifi smart thermostat and realized while I have 3 wires hooked up to my old thermostat, the common wire is not hooked up to anything in the basement. I'm wondering if I can ...
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1answer
91 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
52 views

installing ecobee SmartThermostat with Voice Control on older home

I recently purchased the most recent ecobee Smart Thermostat with Voice Control. The existing thermostat needs to be updated. However, I'm not sure if I'm able to install this without installing the ...
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3answers
498 views

Using a ground wire as a thermostat C

Just theoretically, A C wire is just a return for 24v transformer right? So if you were in a situation where you have access to the slab, or just a standard outlet or switch receptacle could you wire ...
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1answer
758 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
967 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
38 views

Can I pull a c-wire from a second nearby thermostat?

I have a thermostat that controls the AC/Heat upstairs which is located on my bedroom wall. Right below that I have another Millivolt thermostat for the gas fireplace in my bedroom. If I want to ...
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1answer
719 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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2answers
3k 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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1answer
81 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
109 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
87 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
50 views

Honeywell RTH9585WF Thermostat wiring question

My old thermostat LUXPRO TX 9600tsa uses 4 wires: W white G green R red hooked to RH and looped to RC and Y yellow This thing is not working right, so I purchased a Honeywell RTH9585WF WiFi ...
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1answer
71 views

No C wire on furnace

I’m trying to connect a C wire to my Nest Thermostat. However, I’m confused on where to connect it on my furnace seeing that there’s no marked slots on my old furnace. Any help would be greatly ...
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2answers
7k 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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0answers
75 views

Not sure where to connect C wire on furnace

I have a Nest 3rd gen thermostat running heat and AC and I even have an extra wire running to the thermostat (5 in all). One wire at the thermostat wiring box is available to use as the C wire, but I ...
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1answer
923 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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1answer
82 views

Air conditioner locating c wire on old unit

Hi guys I'm trying to figure out I'm using a dual heat and cool thermostat so i decided to get myself a smart thermostat and want to connect both thermostats into 1 but I'm having trouble location the ...
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1answer
943 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
755 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
1k 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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1answer
64 views

Low Voltage C-Wire at Thermostat

Looking to install an ecobee thermostat and decided to measure my common wire before unhooking anything. I tested the R, C wires and see they are only reading 14v, whereas R,Y, and R,W are reading 28v....
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1answer
121 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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