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
43 views

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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48 views

Honeywell 5-wire zone valve wiring

Update: I was able to successfully re-wire a spare wire to my Google Nest Thermostat 2020 AND reconnect power to the C-Wire of my 3rd generation Nest Learning Thermostat. Turns out the 3-amp fuse in ...
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1k views

C wire and smart thermostat

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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45 views

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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397 views

Reznor UDP-60 - Need C Wire

I read the following but my situation is slightly different: Wifi Thermostat to Reznor Garage Heater. No "C" wire connection on terminal strip He had an unused wire connected to W2. I want ...
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53 views

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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3answers
133 views

Does this seem like the right place to tap a C-Wire from my heater?

I need a C-wire for my thermostat but my heater only has R and W connectors (red circle). On the schematic on the heater, up top (red arrow), looks like: 5 is 24V Gnd (bit hard to read but i've ...
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52 views

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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67 views

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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1answer
3k views

Adding C-Wire for Nest to Triple Aquastat Relay L8148J

Need some extra eyes and advice on how to add a common wire to our current boiler setup. We have a Triple Aquastat L8148E that has 2 wire that connect to our thermostat. Like many before me, I'm ...
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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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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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461 views

Where do I connect a C-wire to my electric boiler ( Slant/Fin Monitron Boiler )

I'm looking to add a C-wire for my thermostat. My current thermostat has two wires, W and R. But there is another tucked in blue wire. That blue wire isn't connected to the boiler. I'm looking for ...
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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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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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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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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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1answer
247 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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2answers
10k 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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299 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
63 views

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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1k 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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6k 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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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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346 views

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
73 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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55 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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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
50 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
2k 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
775 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
80 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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1answer
71 views

Adding a C wire for WiFi Thermostat

I have a secondary transformer already which is supplying power to my 2 zone zoning board. Can I tap off of this to provide my WiFi thermostat with power or does it have to come off the furnace board?...
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1answer
54 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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2answers
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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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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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117 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
138 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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164 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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2answers
1k 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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38 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
38 views

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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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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54 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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890 views

Connecting a C-wire to a Burnham Independence Boiler

I would like to install a Sensi thermostat which requires a c-wire. I am planning to run a new thermostat wire, since the old one was 18/2. I am trying to figure out the correct way to wire the c-wire ...
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2answers
405 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
62 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
63 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
70 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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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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