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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49 views

Adding a C Wire using a 24V AC Transformer to a 2 Wire Heating System for Nest

Continuation from Can I use any of my existing oil control terminals (TTFFAA) for a C wire? I have an older two wire heating system (R, W). I have 5 wires going from my furnace to my thermostat (only ...
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50 views

Can I use any of my existing oil control terminals (TTFFAA) for a C wire?

I, like many other, similar users on this site, am trying to install a WiFi-enabled thermostat. Hopefully there isn't a prize for oldest system. My current system setup is: Oil furnace (Heat only / ...
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1answer
38 views

OK to use this C-wire in old boiler for Nest smart thermostat?

I have an old heat-only gas system with radiators, the boiler is a Willaimson-Thermoflo GWA070NS. I'm trying to install a Nest thermostat but only the R and W wires were in use with my old one. There'...
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C Wire on Furnace bundled up to go to the thermostat, but not on Thermostat?

I just moved into a new home and wanted to install a smart Thermostat, upon checking behind my current thermostat I noticed that there was no C- Wire, so I checked the Furnace, and saw a C-Wire, which ...
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1answer
42 views

What Do I Lose With a Honeywell C-wire Adapter?

I'm upgrading to a smart thermostat, which requires a C wire. My current thermostat cable has 4 wires, no C wire. The controller in the furnace does have a C connection. The system has both heat and ...
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How to create a C-Wire from Honeywell R8888A/B

So Ive been trying to install a new Honeywell wi-fi thermostat. I have been unsuccessful in any event. I have a third wire unused at every thermostat in my home which is black. This black wire tuns ...
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1answer
85 views

How to connect C-Wire to Weil-McLain Boiler CGa Series 3

I'm trying to install a Nest learning WIFI thermostat to my boiler. However, I'm not sure where to connect the common wire. I've went through multiple posts on this forum but unfortunately wasn't able ...
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96 views

Can a thermostats C-wire be connected to the furnaces R-terminal without issues?

I was looking around at my furnace wiring to see if my C-wire was connected on the furnace side and noticed that the C-wire from the thermostat goes to the R-terminal on the furnace. This doesn't ...
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Another c-wire challenge

Opened the furnace to find this situation: Red and white coming in from the left are from the thermostat. Yellow wire nut is labeled C. Other end is in the circuit board. What do I connect the C-wire ...
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30 views

Smart Thermostat - Boiler does not have a C terminal. Can I use the TV or T instead

I am trying to install an Amazon smart thermostat but the boiler does not have a C terminal. It has a C1 terminal but I do not think it is the same due to it being connected to the circulator pump (I ...
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1answer
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An issue with Installing C connector to the Weil McLain boiler

I'm trying to install a C connector to my Weil McLain boiler. The C connector instruction seems simple. Just connect all Ws to Ws, and Rs to Rs as the picture below. but the wiring in my boiler seems ...
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1answer
54 views

Connecting a Google Nest Power Connector to Lennox GSB8-E

Installing Nest thermostat, getting no c-wire error. Get the nest power connector, to attach to the circuit board of the boiler......and that is where I get lost. Green wire in center has 24V ...
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1answer
40 views

Fast Stat Common Maker Setup on 2 Wire Boiler

I'm trying to wire up my ecobee in a new house that only has 2 thermostat wires (R, W). I bought a Fast Stat, but I'm unsure how to set it up as I have a complicated setup. There are two aquastats (...
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Where can I connect c wire from adaptor if I don’t have c terminal in my boiler control board

I was wondering if someone can help, I have an IBC boiler (heating only) and trying to install a smart Google thermostat that requires a c wire. I also got the Google nest power adapter where you put ...
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1answer
47 views

No “c” wire terminal on my furnace

My furnace doesn’t seem to have a “c” terminal I can hook up my adapter to for the nest smart thermostat. My terminals are numbered instead of lettered. I tried them both but the thermostat still had ...
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1answer
50 views

Installing a Nest Thermostat can't find circuit board

Hello so recently I have been wanting to install one of these nest thermostats into my home and realized I didn't have a C wire and it was recommended to install a google nest power connector, the ...
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C wire possibly on my boiler/heat pump

Hey so I know this is annoying and asked way too often but the wife wants a WiFi thermostat and of course I don’t have a “c” wire hooked up and there is no “c” terminal on my control board. We have ...
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Want to add a C-wire to a ClimateMaster Compact Heat Pump in combination with a Nest learning thermostat

My existing Nest learning thermostat, 3rd gen, is draining the battery really fast when use the wifi. I have a ClimateMaster Water Source Heat Pump. It has only four wires. I run an extra wire to ...
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1answer
93 views

Nest Thermostat Wiring problem - Heat does not work

I recently replaced my old American Standard thermostat with Google Nest. Cooling works fine but Heat does not work and simply goes into an unending loop of 'delayed: will start in 2:30 secs' I think ...
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1answer
34 views

Neutral Wire on Oil Boiler

I am going to help out a friend hook up their nest thermostat and as you might have guessed it's only a 2 wire at the location of the thermostat. Since the cheaper and newer version of the Nest ...
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1answer
38 views

For Nest Thermostat, Can I use new wire from T to C?

Old Thermostat had no C connected to it but furnace has T with wires and there is an extra wire wrapped around at the furnace and at the Thermostat. Can I just attach to T terminal and C on the Nest? [...
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1answer
75 views

Google Nest C wire Blues

Can anyone help with my c wire blues with my Google Nest? I have two ACs, one for downstairs and another one for upstairs. I recently upgraded my battery operated t-stats with Nest. My old ones used ...
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Wifi Thermostat "C" Wire - Separate A/C & Heater System - Connection Conflict

My Honeywell Thermostat WiFi System via the "C" Wire was working correctly when the "C-WIRE" was hooked to the A/C Unit. I needed to change the "C" Wire to my Gas heating ...
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3answers
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Adding a C wire or Google Power Connector to an old Lennox furnace

As the title suggests I am looking for advice on connecting a C wire or hooking up a Google Power Connector (I have it already) to my furnace. I have a Lennox G803, it already has a humidifier ...
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1answer
54 views

Ecobee 3 Lite Installation - No C Wire, only 3 labeled wires on Furnace board

Trying to install an Ecobee 3 Lite thermostat. The old thermostat had a W, G, R, and Y wire connected, but no C cable which is needed. However, I saw an unused red and blue wire in the wall and ...
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1answer
31 views

Adding a C wire to Lochinvar Boiler - 2 zones

I am trying to connect an ecobee which requires a C wire to my 2 zone heating system - boiler is a brand new Lonchinvar. My current thermostat only has a red and white wire (I have no AC, just heat). ...
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2answers
124 views

Please help me find the right spot to tap into for C wire at the furnace

I am trying to upgrade our thermostat to a Wifi unit that needs a C-wire. Found the unused C wire at the thermostat end and connected it. AC wouldn't power on, went to furnace end and found it wasn'...
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1answer
38 views

28V at furnace, 0V at previously working thermostat

This is a followup to an earlier question I posted where it appeared that the previously unused Common wire on my HVAC system was damaged. All of the other wires read 28V between them and R, and the ...
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1answer
89 views

Low voltage over C wire at thermostat

Similarly to this question of the same name, I am reading low voltage over the R,C wires at the thermostat. Unlike that question, however, the voltage is unusably low. I am only reading 2V over R,C ...
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42 views

Identify HW aquastat and add common wire to Honeywell aquastat

This has been asked before, but I can't find any info on my Honeywell aquastat. The model number, normally on the inside paper on inside of cover, is missing so I do not have any model number. There ...
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2answers
224 views

Adding a C wire for a Nest thermostat

I tried upgrading to a Nest thermostat, and that's how I discovered I don't have a C wire... I'm thinking how to add it. I have some interesting situation: single furnace, and 4 zones connected to it ...
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HVAC Blower Fan stays on ALL THE TIME - Even when the system is off

My HVAC Blower fan stays on even when I remove the thermostat face plate (with the fan in the auto position and the thermostat in the off position). I have tested for a short in the thermostat wire ...
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24 views

C wire not identified

I have the c wire which I removed and reinserted but still the thermostat showing error that its not identified
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1answer
61 views

Smart Thermostat with TWE040E13FB2

I have a trane TWE040E13FB2 hooked up to a heat pump. I am wanting to install a smart thermostat. Our current thermostat has 10 wires in it. I do not have a common wire. I also don't see a common wire ...
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24 views

Refrigerator Compressor not working?

I unplugged then plugged back in my fridge an it isn't cooling or freezing! Does that mean my compressor is no more working? The light comes on inside the icebox?? Just not cooling or freezing..
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1answer
31 views

Hvac/thermostat wiring questions and problems

I have a modular home. My hvac system is a heat pump/ac with emergency heat strips. It has 5 wires in the wall and my thermostat is battery operated. I want to install a new Honeywell thermostat with ...
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2answers
80 views

Installing c wire in older furnace

I just installed a nest thermostat and need to hookup the c wire inside the furnace. I read where you need to connect the c wire to the secondary wire on the 24v side of the transformer. There are 2 ...
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60 views

C wire for wifi thermostat

I'm at a loss. I have a wifi thermostat to install. No c wire connected so a 4 wire thermostat but have 4 additional wires unused. I checked our Goodman ac/furnace and found the unused blue wire. The ...
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1answer
28 views

Swap 2nd thermostat for *off* swtich downstream of 1st thermostat

I have two thermostats running two different fans wired up like this: I'd like to replace the 2nd thermostat (on the right, in box #2) with a switch. I have done this and have the ability to turn Fan ...
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2answers
67 views

I need a C wire connection for my new Glas thermostat

I have 3 wires(red,white,and green) going to my thermostat. I’m replacing my old thermostat with a new one the requires a C wire connection. The 3 wires goes to my Honeywell aquastat. The white goes ...
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1answer
167 views

Help needed on thermostat wiring with Ecobee and Fast-Stat 5000

I'm trying to replace existing Honeywell controller for my furnace with Ecobee 3. The Honeywell controller does not use a C wire, however there are a black wire and blue wire in the wall behind the ...
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1answer
47 views

C-wire on Weil McLain cGA Gold has low voltage

I am trying to run a new c-wire for my new ecobee thermostat. When I finished running the c-wire from the thermostat it did not turn on. I tested the voltage at the boiler and it is only reading 17ac ...
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0answers
374 views

Nest 3rd gen thermostat N72 Error Does not detect Power from Rh wire

I just hooked my Nest 3rd gen thermostat to my split heating/cooling system with a Common wire coming from the air handler in my ceiling. On my old stat I didnt use a common because it was battery ...
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64 views

Is this blue wire in my A/C a C wire I can use at the thermostat?

Here's my current setup - separate A/C and boiler units. Some of the pictures may be confusing because the wires are differently colored than they're named, but I'm going by my actual thermostat. ...
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30 views

Trying to wire for Ecobee thermostat

I have an ecobee thermostat I'm trying to hook up, but I can't figure the wiring out. We have fuel-oil boiler and an AC, with the oil boiler using radiant water pipes (as well as heating our water for ...
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78 views

C-wire nest to burnham boiler

Connecting nest learning 3rd gen to burnham series 2 model 203 boiler. I am only using the system for heat. I have three wires at the thermostat R,W and an unused green that I would like to turn ...
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1answer
55 views

How do I determine which is my common C wire?

I am trying to install a Nest Thermostat and I need some help locating which of the wires would be the common "C" wire. I have traced all the wires going from the thermostat, condensate ...
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2answers
58 views

C wire possible for Nest thermostat?

I have a Nest Learning thermostat. Recently, it has caused a clicking sound to emanate from the furnace area whenever the system is powered off. I've determined this is due to the thermostat drawing ...
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3answers
195 views

Where can I install a C-Wire for Weil-McLain gas boiler? (EGH 115, 4 Series, Natural gas)

I want to install a C-wire so that I can use a WiFi Thermostat. Behind my current thermostat there are only 2 wires (red and white) There are 2 wires tucked and unused, (green and blue) I had tried ...
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88 views

C Wire - Williamson Furnace/Honeywell Thermostat

I'm trying to install a new wifi thermostat, but am a little confused. I have 5 wires, but none are connected to the C in the thermostat, as seen below: Additionally, when I trace the thermostat to ...

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