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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34 views

Adding C Wire as simple as C to C?

Short version: I ran a new 2-strand wire from my thermostat to the furnace/air handler unit to provide spare wires since the existing 5 wires are used up and I need a C. Is hooking up the C wire as ...
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46 views

Wiring Ecobee thermostat to Vulkan gas furnace with no C terminal

I am trying to wire up an Ecobee thermostat to an old (1997) Gas central heating system but I got up into the roof then realised I have no terminal labelled C. Now, I don't super know what I am doing, ...
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132 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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183 views

How does this wiring work?

I have a Trane XV90 and XL 14i. The wiring looks a little strange as in the picture bellow. _____________ | | BK W2 W1 R G Y B/C YLO O |___||...
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250 views

how to add c wire to heat pump ac unit (only have wires with nuts)

I can’t figure out which is the C wire or how to make a C wire and how to connect it to my ecobee 3lite Power extender kit. My old thermostat has wires G,Y,RH, W/E, and O/B plugged in. No "C"...
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294 views

Is this wiring dangerous? Smart Thermostat C-wire AC adapter twisted together

Is this wiring scenario dangerous? Is it likely produce sparks or damage my HVAC system? Please read the description and see the image below. Description I didn't have a C-wire for my Emerson Sensi ...
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83 views

Honeywell C wire on a dual transformer system

Currently I have dual transformer system From heat >> RH & W1 From cool >> Y1, Rc, G Honeywell provides a C wire adapter and also mentioned turning an unused wire into a C-wire. I do ...
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965 views

Where to connect C wire if no C terminal

Hi wanting to connect Nest and want to install a C wire. HVAC only appears to have G,W,R so not sure where to connect C.
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431 views

Getting power to Nest Thermostat E from 24V AC transformer

My baseboard hot water system lacks a C wire connecting the transformer at the boiler to the thermostats for any of the zones. I cannot readily run additional wiring between the transformer and the ...
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61 views

How can I install a smart thermostat with my HVAC system?

I have a Ruud furnace / air handler with a non-programmable thermostat installed. It looks to be a model RGPE-07EBRQR (Rheem?). I want to put in an Ecobee and am a bit confused about the wiring. ...
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691 views

Help connecting unused C wire for Smart Thermostat

Looking to connect a newer WiFi thermostat which requires the connection of a c wire. My old thermostat didn’t use a c wire however there is a c wire present in the bundle of wires ( unconnected at ...
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132 views

C Wire doesn’t work

Trying to swap an old Honeywell thermostat for new with Wi-Fi. Old thermostat doesn’t need C wire, but I have an unused blue wire in the wall. I installed the new thermostat correctly with the C wire, ...
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862 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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163 views

Ecobee 4 - C Wire Connected but no power

I have an extremely old HVAC system (Goodman Janitrol Model GMNT060-3) and had a previous WiFi thermostat connected with a C Wire. I am now upgrading to a ecobee4 and cannot get any power to the ...
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156 views

Connect "C" wire on boiler model number 1135-601

I've read several threads here and on the other websites but still can't figure out how to add C wire to my boiler wiring. I would like to replace my old mercury thermostat with Nest E or any other ...
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1answer
74 views

Emerson Sensi Touch C wire help needed

I am heating with a fuel oil boiler in the basement and a Unico air conditioning unit in the attic. I some help getting past the c wire issue. Air is using yellow, green and red-c and heat is using ...
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5k views

Why is Thermostat Y wire connected to C terminal on furnace?

I have a Nest E thermostat, and like many others have lost wifi and getting low battery because I have no common wire connected. After looking at my old Lennnox 78ugf3-75-1 furnace, I noticed that my ...
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360 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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313 views

Can a C wire be used for two 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 cables running from 2 units to 2 ...
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56 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
87 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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729 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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419 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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387 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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124 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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30 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
235 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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1answer
153 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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145 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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2answers
687 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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2k 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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151 views

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

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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69 views

Add "C" wire to NEST

I have a NEST thermostat. My heating and cooling system is in the attic.I need to add a "C" wire to the control board, but I can't find out where I need to open the unit in the attic to see where the ...
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1answer
181 views

Wiring HVAC for smart thermostat

I'd like to install a smart thermostat in place of my old mercury coil thermostat. The old thermostat controls both heat and AC - it uses only 4 wires, the new clearly requires 5. Wiring to the ...
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642 views

No C Wire Nest Thermostat

I just installed a nest thermostat. The previous thermostat did not have a C wire attached. It G, RC, (RH Jumper), Y and W. When I hooked up the nest thermostat it was short cycling the blower fan ...
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641 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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185 views

Adding a C Wire for my new thermostat

I just bought a thermostat that needs a c wire. I ran a 18/5 wire, but where do I connect the c wire to? Here is a picture of the back of the board.
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76 views

Wired "like" a dual transformer

I'm trying to update to a smart thermostat and my current one is wired like a dual transformer but I only have a single hvac system in the basement. Any idea why? My plan is to move the blackwire ...
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57 views

upstairs furnace stopped working after connecting c-wires to both HVACs for ecobee 4 downstairs

My AC/heater for upstairs rooms used to work. But after connecting the c-wires to both HVACs in the attic it can no longer be started with the LED controller. I probably should have connected only one ...
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93 views

Thermostat/Furnace Wiring Confirmation

Like so many others, I am looking to install a new wifi thermostat with an older furnace. I've searched across the Internet and I have a pretty good idea of what is needed and why; however, I have a ...
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2answers
1k views

Where to connect a C wire for my smart thermostat

I am trying to connect the c wire but I'm at a crossroads of sorts. I have a dual zone so there are 2 thermostat wires come into what looks like a relay box ( see pictures) I have located the ...
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162 views

HVAC: Nest - Yet another 'C' wire question

I have a dual transformer system. At the AC/Blower unit, there are 'R_c', 'Y' and 'G' wires; there's 0VAC between the 'Y' and 'G' wires, and each shows 27VAC to the 'R_c' wire. At the boiler, there ...
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402 views

Red wire in place of C-WIRE?

I just moved into a new home and was trying to connect my Ecobee thermostat. I know it requires a C-wire. I found the wire wrapped around the others in the previous thermostat, which didn't require ...
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1answer
847 views

Connecting thermostat common wire to air handler or boiler?

we are planning to install a Nest learning thermostat in our house. On first installation attempt the device notified us that there was no power from the Rh or Rc wires which from my understanding is ...
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220 views

How to add a C wire to an old Lennox attic furnace GS810-105N

I bought a smart thermostat for my house in hopes of cutting some bills a little. I read up on them, I thought, thoroughly and figured I could handle the task. However, upon climbing up in the attic ...
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270 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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936 views

Where do I connect C-wire to Burnham boiler?

I'm adding a smart thermostat to one zone of a two wire, oil fired boiler system. I've roughed in a new wire and could use some help determining where to terminate it at the boiler. The wiring is far ...
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2answers
1k views

Need help with 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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2answers
4k views

How do you install a thermostat if you don't have Y or C wires?

My thermostat is a LuxPro LUX PSP511LCa. I looked behind the thermostat and I see the following: A red wire connected to RC A jumper connecting RH and RC A white wire connected to W A green wire ...
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839 views

Adding a C wire and fixing White vs Red on my Furnace

TLDR: I think I need to flip R and W wires, and to splice the blue (C) wire to the brown wire coming of the transformer. Is this correct? Long version: Like many others on here, I'm trying to add a ...

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