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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Advice on how to wire a 4 wire RGWY wifi thermostat to an old hvac with no c wire?

I have a 4 wire RGWY coming out of the wall to my old thermostat with no additional wire available for c wire. I was going to use the green one instead as I saw a tutorial online, but when I got to ...
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Where do I connect my common wire (C wire) for smart thermostat?

I've been running 2 Nest thermostats (1 upstairs, 1 downstairs) for years that didn't require a common wire. I'm replacing them now with Ecobee3 Lite thermostats. Both thermostats control heat from ...
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How can I tell if my current thermostat wiring has a C wire?

We just moved into a new house and I want to replace the thermostat. I am trying to figure out if my current setup has a C Wire. If it doesn't, then I'll need to get a new wire run -- which I want to ...
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Where to connect the C Wire? See pictures and diagram [duplicate]

I have Rheem RBHC-14A00NFA AC unit. I am trying to install nest thermostat but don’t know where to connect the C wire. I am attaching the picture of the wires and the diagram. Please help! Thanks
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Adding a c-wire to a Goodman A30-10C for smart thermostat

Looking for a little help installing a c-wire on my Goodman A30-10C so I can run a new Sensi smart thermostat. I currently don’t have a c-wire running to the thermostat, and don’t really know where to ...
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I am trying to connect a c wire to my crown furnace that is use only for radiant floor heat. I do not know where to hook it up to

I am trying to install a densi smart thermostat with a c wire. I do have the c wire available but not hooked up. The older honeywell thermostat only had 2 wires red[R] and white[w]. At my crown ...
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Furnace doesn’t have a c wire and or board

Have an old Colman unit in a modular home, needing to hook up c wire adapter. Does not have a circuit board. Any help on trying to hook up c wire would be great. Tried loading photo but will not let ...
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No C wire for Nest thermostat but unused C terminal on furnace

I know this question is similar to others I’m just hoping for a short answer. It’s a small house and the thermostat and furnace might be twenty feet apart. The control board on the furnace has an ...
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Separate Boiler & AC system and WiFi thermostat

Wiring to Honeywell T9 WiFi thermostat. Have separate hot water boiler and separate Trane AC air handler to outside compressor. Trane AH has no board only colored wires Blue Green Red Where is the ...
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C Wire for Weil-McLain Ultra 105 series 2 location?

Recently bought a home with a Weil-McLain ultra 105 series 2 boiler. I’m looking at relocating the thermostat and putting in a smart thermostat. My questions is I’ve never seen one with a low voltage ...
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Existing thermostat wire colors - no white?

Looking to switch from an old Honeywell CT87A thermostat to a smart thermostat, probably something requiring a common wire. There are 2 thermostats (one on each floor) in a 2 zone forced hot water oil ...
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Ecobee 3 Lite / Fan Center for Fan Coil / Aquastat

I live in an ancient (1967) condo with a two-pipe system. Cold supply in the summer, hot supply in the winter. There is no electronic changeover or even an automatic cutoff valve. The radiator coil ...
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1 answer
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Lennox Wiring for Ecobee SmartThermostat

Confused by the wiring, hope someone can help me out. At the furnace there's only four wires in the cable (R, B, G, and W), but at the other end, a yellow wire appears. It's not reflected in the ...
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Is it possible that Thermostat Y wire and C wire is the same wire on my air handler (furnace)?

I'm trying to install Ecobee, and like many others, I do not have C wire at the thermostat, thus need to find it on my air handler. My air handler is from Allstyle and the model number is HFD36-42840G-...
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Can I pigtail a "C" common wire to power a Smart Thermostat to the 24v wires coming from the outside AC compressor?

Hoping someone can help me solve for powering a 24v Common wire to what will be my new smart thermostat. Currently my downstairs thermostat controls a boiler as well as the central air unit for ...
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Common wire for installing smart thermostat(Amazon thermostat)

I'm trying to install the Amazon thermostat to replace a mercury switch thermostat. The existing wiring has yellow, white, green, red and once the wall plate was removed there is a blue wire untouched....
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Ecobee 4 thermostat with Slant fin Monitron Boiler - No C wire

I want to replace my thermostat (Honeywell th1100dv1000) for an Ecobee 4 but it needs a C-Wire. I own a Slant Fin Monitron Electric boiler currently running with only two wires (R and W). I have a ...
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Add C wire to very old gas furnace

There is a very old gas furnace in our attic. It has a two-wire transformer and no obvious terminals to expand. I need to run a C wire to my nest thermostat, which I'm planning to do via their nest ...
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C wire confusion

I have an old thermostat (20 + yrs old) that I want to replace with a Sensi smart thermostat. My furnace has a dull pink looking wire connected to the W terminal (also connected to the W on the old ...
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Blue wire in Y: Thermostat wired right?

I recently purchased a new property, and I noticed the thermostat's blue wire is in the Y terminal. Reading online, the blue wire is typically in C. Is my thermostat wired correctly? For reference, my ...
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How to get the C wire for Nest thermostat on Burnham series 2 gas boiler

I am trying to setup a smart thermostat for my boiler. Can you help me see where I can extract the C wire out from my boiler. Thanks
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Blue wire is used on furnace, but not thermostat

When I looked at the wires behind the thermostat, the blue wire wasn’t used. However when I look at the furnace, the blue wire is connected. I’m not sure if I should use that as the C wire. I did try ...
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Adding New External 24v Transformer to Nest with separate Rh and Rc wires

I have separate heat and cooling systems with wiring to Y, W, G, Rh and Rc (see below). For the external transformer, where do I attach the two wires. C and ?
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Would it be dangerous to tap an existing flame sensor circuit to create a common connection for my thermostat?

I'm considering using this answer to connect a common wire to my thermostat. I have the exact same setup, and have verified with my multimiter that the red T terminal outside F terminal beeps, while ...
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Honeywell 5-wire zone valve wiring

TL;DR Is a jumper wire necessary between TH/TR and the left-hand END SWITCH? If so, what does it do? As requested, here is my best approximation of a wiring diagram: As it is now (note the missing ...
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Thermostat replacement, no c wire

I have an almost 20 year old Taco thermostat that I am trying to replace with a Nest thermostat for a forced hot water heating system. The Nest requires a W, R, and common wire, current only uses W ...
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Is it possible to add a C-wire to a Honeywell R7284 Oil Primary Control (current two-wire system)?

I currently have a two-wire system (R/W) going to my thermostat. The furnace is an oil heat system with a blower to force air. There is currently a Honeywell R7284 Oil Primary Control where the ...
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Not getting power to a new C Wire

I am trying to finish installation of a new nest thermostat and ran into the dreaded “no C wire” issue. After reviewing several posts here, I felt pretty confident that with my new-ish furnace I could ...
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Where to connect common wire from thermostat to First Co. air handler?

I'm trying to install a new Honeywell WiFi 9000 thermostat which requires a common wire. When I removed my old thermostat, I can see there are two extra wires in my wall (black and orange wire) that ...
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Wiring Boiler for a C wire Adapter

I want to install a smart thermostat for one of my boiler zones. My thermostat doesn't have a C wire. It looks like installing an adapter would be the best option, but I am not sure my system is ...
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Nest and ZVC404-4

I am trying to update my thermostat to Nest. Get 4 Nest but could not get it working at all. The HVAC control board actually have C-wire (it was not used previously, I connected it when I start the ...
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2 votes
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Connecting C-wire to Nest Thermostat for Lennox HVAC

My Nest thermostat has been running fine for quite a while, but recently it started complaining about low battery and wi-fi gets shut down due to power issues. I've been looking for the answer, and I ...
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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? EDIT: Wanted to finally say this is SOLVED with help from @JPhi1618 (see conversation below). If you have a ...
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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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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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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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1 answer
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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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1 answer
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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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1 vote
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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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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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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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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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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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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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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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