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
53 views

Ecobee reports wiring error on Lennox furnace

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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17 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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25 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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51 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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26 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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27 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
42 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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43 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
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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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57 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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Adding c wire to old furnace

So some background, converting from an oil to a gas furnace and was looking at adding a smart thermostat. Two things that kind of raised questions and I cant seem to find much answers too. One is the ...
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34 views

Will a nest work for my hvac system

I have a heat pump system and would like to get a nest thermostat. On my system I have to switch it from heat to cold. See picture of wiring. If a nest won’t work what WiFi enable one will work.
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19 views

Two Sets of Wires on HVAC Panel

Ultimately I'm looking to use a C wire for a Nest thermostat, but upon looking at the HVAC panel I'm confused by the wiring. There's a grouping of wires going from the HVAC panel to the thermostat: ...
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58 views

C-Wire Williamson gsa-125-n-ip

Looking to install a C-wire for my power stealing nest. I have 5 wires up at the thermostat and same at the boiler. I am using red and white at the thermostat however it looks like blue and white it’s ...
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35 views

Hooking up Ecobee smart thermostat

I purchased a new Ecobee thermostat. I don't have central air, so heat only. My gas fired hot water boiler has the wires from the thermostats (Red and White) going to the T1/T1 and T2/T2 terminals. ...
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Replacing my Honeywell thermostat with a Nest heatlink in the UK

Can someone help with this. Trying to pick the C wire and the NO wire from here. Please note I am in the UK
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2answers
47 views

Adding the c wire to a two wire system

I purchased a RTH9585WF smart color thermostat to replace my mercury controlled thermostat. How do I add the blue common wire at the boiler relay where the two wire system is connected? ://i.stack....
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159 views

2 wire smart thermostat nest but no RC or RH

I just got the new 2020 model nest and i was going to do the 24v transformer suggestion in other thread but these new models do not have RC or RH on them. they only have Y,G,R,W,C,O/B. Will the ...
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What is causing my ac unit and thermostat not to work with one another

Inside unit and thermostat are not working properly. In the beginning, something needed to be changed in it,it was a small black box and a round cylinder like plug thing.changed out the thermostat ...
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95 views

Connected C-Wire (previously unused) to thermostat, but still no power?

In search of help with hooking up a Nest Thermostat E. I have seen several threads seeking solutions for similar issues and have troubleshooted with their proposed solutions with no luck. I am ...
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41 views

C-Wire for thermostat

My furnace is a gmp075-3 There is an existing unused Blue wire coming from the thermostat to the furnace area but not attached to anything. (upper blue wire in 2nd image) Can I just connect the upper ...
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1answer
54 views

Connecting blue “C” wire to gas furnace, but furnace already has white wire?

sorry if this is a stupid question but I'm trying to install a smart thermostat (Nest). I realized that while there was an unused blue "C" wire behind my old thermostat, it was not connected ...
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54 views

C-wire help needed with Nest thermostat install

My air handler (see photo) connections are G,W,Y,R and COM. The a/c compressor (outside) is connected to air handler Y and COM. I have 5 wires out to the thermostat, G,W,Y,Rh with jumper to Rc, and an ...
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119 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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155 views

Burning smell from AC vents after installing new thermostat

I was installing a new thermostat (ecobee3 lite Smart Thermostat, 2nd gen) to my AC unit (ARUF61D14AA). I opened my current thermostat and noticed that I don't have a C-wire (which is required for the ...
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2answers
74 views

Using red wire for smart thermostat voltage

I want to add a smart thermostat. Why can’t I use the red wire voltage for the c wire? I’ve read where some say red wire is intermittent voltage, but mines constant.
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1answer
82 views

Adding C wire for wireless thermostat

I'm trying to install a new wireless thermostat but my old setup only uses 2 wires; one white and one red. On the side of my furnace there is this transformer mounted. There are four cables on the ...
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1answer
45 views

Thermostat C wiring issue

I am having a two-wire system oil boiler with two-zone valves. I installed two Nest E and worked fine but it started to swing the valves due to the charging cycle. So I decided to run a new C wire ...
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1answer
103 views

Where would I connect the C wire in my HVAC system?

I'm upgrading the thermostat with a Eco Bee WIFI one. Where do I connect the C cable? (Rheem 15 to 20 years old.)
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3answers
212 views

How do you estimate the probability of failure in this case? [closed]

The fan relay draws 6.0A. That is a safe current for 16 gauge wire. The safety fuse is tripped at 15A which is too much 16 gauge wire. This installation guide shows the Installation Instructions for ...
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1answer
74 views

Help running a C wire from my furnace--no voltage from the C terminal on the circuit board

I am thinking about changing thermostats for my ICP END4X36T17A2 furnace, but my options are pretty limited due to my current thermostat hookup lacking a C wire. It currently has four wires hooked up ...
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129 views

help me find C wire on williamson boiler and where should I connect it

I have Williamson boiler GWA 140,000 BTU. I have 2 zones in my house for heating. On one zone I want to install smart thermostat so, I need C wire. The old thermostat for this zone had 2 wires: red ...
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59 views

Where do I connect my new T-Stat in my Weil Mclain boiler

I have a new smart thermostat and looking to connect to my boiler. As you can see in the picture there are (2) yellow wires which are labeled 24v control. One yellow wire is connected to the Y ...
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227 views

c wire on a multi taco zone valve boiler

looking for assurance on what I think is the right setup to add a c wire to a current 2 wire zone setup. See pic of transformer junction box. Currently I have 3 zones using one transformer and 3 taco ...
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1answer
75 views

Goodman - C wire connection

I have an older unit Goodman furnace with a c-wire that isn't connected to the unit. In order to install a wifi thermostat to supply continuous power I need to connect the c wire. I see spots for the ...
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1answer
62 views

What can I use as a C wire for my new thermostat?

I currently just installed the nest e thermostat which replaced an older Honeywell thermostat for my older oil furnace. I connected the Red and a white wire to the new thermostat and it worked for a ...
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103 views

Problems w/ Nest

I've got a common problem but I can't seem to find the simple answer. My heating system is simple. Forced water oil boiler with three zones. Two zones are controlled by the Nest E Thermostat. I'm ...
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1answer
174 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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88 views

Thermostat C-wire not working

I recently switched out my old thermostat for a new thermostat. The previous thermostat had an R, Y, W, G, and C wire. I plugged all of these wires into the same ports on my new thermostat. After ...
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49 views

Where should I place the C wire?

I have an old Lennox boiler which doesn't appear to have a PCB board. Originally the old honeywell thermostat had a 2 pair wire attached which included Red and White Wires. I snaked an 18/5 thermostat ...
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1answer
235 views

Connect C wire for nest thermostat on a zoned HVAC system

I got a nest thermostat which requires to get a C wire. My old thermostat does not have c-wire connected, but there are four unconnected wires as shown in the picture. Then I came to my furnace and ...
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28 views

Where to connect common wire (no C terminal at furnace)

Trying to add a c wire for my nest thermostat and I have a free wire in the bundle (blue) but there isn't a c terminal at the furnace. I know there have been similar questions just want to ensure I ...
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1answer
88 views

Where to add C wire on transformer?

I want to add a C wire to support a smart thermostat. The existing wire is 2-conductor (R+W). I can run a new 18/3 easily, but I don't see an obvious place to attach the new C wire on the burner/...
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63 views

C wire for a smart thermostat

I would like to buy a smart thermostat and I am confused about the C wire. I went to check my furnace in the attic and I saw a white wire connected to the C, I was excited as I thought that that was ...
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170 views

Can I directly add a Common wire to this point on a 24VAC transformer, or will load be too high? (70mA)

Referencing This excellent answer I have a two wire furnace controller, 24VAC, no common. I measured the current draw of the relay (when the thermostat wires are shorted), it draws 0.2A Wish to add an ...
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145 views

HVAC: adding a C wire for Nest thermostat

Just installed a brand new gas boiler, want to keep using my existing Nest thermostat (they are compatible according to Nest). Current system only has two wires: Rh and W Nest is designed to steal ...
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274 views

Thermostat wiring identification - missing yellow wire/extra wires

Help please and apologies in advance for lack of technical knowledge! I'm looking to replace my old Honeywell 8022C 24v thermostat with a Nest, and have failed on several levels now I've taken a look ...
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134 views

Rewiring a boiler’s c wire for a smart thermostat

I want to swap out my low-voltage Honeywell for a Nest E thermostat. When I took the Honeywell off the wall I confirmed that I’ve got a C wire running up to the thermostat but when I wired up the Nest ...
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new nest thermostat no c wire

I have a new steam boiler model uh1606hsid boiler, I recently bought a nest thermostat and battery keeps dying, is there a way to connect a c-wire to my boiler?
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493 views

Adding Venstar Add-a-wire ACC0410 to HVAC with Nest Thermostat E

I purchased a Nest Thermostat E and found that I don't have C-wire. With the research, including adding venstar to HVAC and Youtube video by Venstar, I tried to add c-wire to my Nest Thermostat E with ...

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