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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2k views

Where to connect my “c” wire on the boiler side. Weil mclain gas boiler

Im just curious if the “c” terminal on the plug in relay is where im suppose to connect my “c” wire on the boiler side. I have 18/5 wire ran already. Just need to find out where to terminate. To the ...
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290 views

Connecting Wood/Electric Furnace to Smart Thermostat

UPDATE: I spoke with an ecobee tech and they pointed me to an alternative solution. If I get an adapter called a "Fast-Stat Common Maker", all I need to do is figure out where to connect the C-Wire ...
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85 views

Ecobee 3 lite Installation — Confusion about C wire (on furnace but not at thuermostat)

I am about to install the ecobee 3 lite thermostat. On the thermostat end, there is no C wire - just the typical 4 wires - R,Y,W,... On the furnace end though, there is white C wire too, which I do ...
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944 views

C wire and smart thermostat (with pictures)

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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837 views

question regarding c wire and a nest

I know this issue has been beaten to death but i am stumped and nest support has no clue how to help me. I thought i had the issue resolved but that was wishful thinking. Here is my issue: I have a ...
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61 views

No C terminal on furnace to connect a wifi thermostat

I have an new Emerson thermostat and would like to connect a c wire so it always has power. I have an extra wire that's not being used, but I don't have a C wire terminal on my furnace. I'm wondering ...
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52 views

Can a C wire be added to an old Teledyne Laars JVT-100C boiler?

Good morning. I have an old Teledyne Laars JVT-100C Boiler, that only has R,W,A terminals. is there a way to add a C wire to this boiler in order to power my thermostats? Thanks in advance...
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Connecting Common Wire from thermostat to Air Handler

My apartment has a central heating/cooling HVAC system consisting of a gas-fired hot water heater which feeds hot water to a First Co air handler for heating, and a rooftop compressor which feeds ...
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Thermostat Upgrade, furnace C-wire reading low voltage

OK so here is the scenario. Upgrading thermostat from dumb to smart (Ecobee). I've done 2 others in my house that required re-wiring so I have a good sense for what should be done but I'm stuck. My ...
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242 views

What terminal to use on AC for C wire / nest dual transformer install

So i purchased a nest gen 3 and proceeded to install it. This is on a dual transformer system, separate boiler and AC system. The good news was i had a unused G wire on the Heat side that I was going ...
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28 views

C Wire to a Dual Zone House

Trying to connect a Nest thermostat in a dual zone house and I need to add a C common wire. There is an extra wire at the thermostat but there is no voltage on it. My current thermostat does not use a ...
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CT80 Thermostat Wiring Diagram Selection

Which terminal should the brown wire be connected to the RadioThermostat CT80? The original thermostat was wired as depicted: The brown wire is connected to terminal E (not F). As I understand it: ...
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328 views

Where to attach the c-wire inside Goodman GMP100-4 Furnace

As a relatively new home-owner, I recently came across the whole C-wire issue for the first time, having had to recently replace an old thermostat, and there is no C-wire connected inside the furnace. ...
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1answer
97 views

need to connect a c wire to my furnace/air conditioner

I installed a nest with 5 wires, but the blue wire is not connected to anything on the 25-30 year old furnace. We tried connecting the blue wire to what we thought was a common terminal, but the ...
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51 views

Where to connect Blue C Wire at old furnace?

I have looked at other responses and each layout is a little different. Looking to connect a Smart Thermostat and need to know where to connect the Blue wire at the Furnace. See the attached picture....
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980 views

Help wiring a Nest thermostat in an unusual situation

The attached picture shows my current wiring. Notice there are two thermostats. The top one (Carrier, with four conductors) controls hot air heating. The bottom one (with two conductors, old mercurty ...
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How can I add a “C” wire to my thermostat?

So, the spiffy new wi-fi thermostats want power on the C wire from thermostat, but the old thermostat doesn't have a C wire at it. What's the easiest way to add the C wire/24 volt to the thermostat ...
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No C wire connection on old Goodman furnace

I have read for hours, and tried figure this out myself, but I need help. I'm trying to connect the Blue C wire from the tstat, without a C terminal at the furnace. From what I have read, it seems ...
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1answer
77 views

How to fish thermostat cable using an existing cable

So I have an existing thermostat cable on my 2nd floor that only has 4 wires, and I need a 5th wire to use as the common wire. Can I use the existing cable to fish or guide a new 6 wire cable through ...
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145 views

C-wire on Weil-McLain CGA Series 2

I have an old thermostat with only 2 wires connected to my Weil-McLain CGA Series 2 boiler. I would like to replace it with a Nest thermostat. I need to add a C-Wire in order for it to work. Luckily, ...
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2k views

Apart from a thermostat, where else can a C-Wire go?

As part of the home work before buying a smart thermostat (yes, because of the standard C-Wire issue!), i noticed that my current old thermostat have only four wires (No C-Wire), but my furnace does ...
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Nest E without common wire stuck in purge loop as soon as the Rheem heat furnace ignites

I have a honeywell hz432 and just installed a few NEST thermostats with a common wire and they seem to run fine. I added another NEST E thermostat, but this one didn't have a common wire, and when it ...
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33 views

Heatpump Wiring Color Convention

A heatpump thermostat is to be upgraded. I am unsure of: Which color wire is the Common (thought to be BLUE) Where should the brown wire be connected? (B node?) Is the 'B' node in the photo ...
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How to add a C-wire to Weil McLain Boiler

I am having trouble installing a new wireless thermostat to my existing Weil McLain boiler. My existing control wire utilized an Rh and W on the thermostat, but utilized the Y and G terminals on the ...
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146 views

Using a ground wire as a thermostat C

Just theoretically, A C wire is just a return for 24v transformer right? So if you were in a situation where you have access to the slab, or just a standard outlet or switch receptacle could you wire ...
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22 views

Thermostat with an external transformer

I am trying to hook up a Vine TJ-610B-W WiFi thermostat to my heater. The original thermostat had only 2 wires, hooked to R and W, none hiding in the wall. I plan to use an external transformer for ...
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8answers
57k views

How can I use a separate transformer to provide a C wire to my thermostat?

Update 02/02/2019 I appreciate all the responses and help but unfortunately i must have not seen the emails stating there were responses! I am now looking into a NEST thermostat and was curious if ...
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37 views

Help adding C wire to furnace - Heat only system

Looking to add C wire into my furnace. Heat is currently running on two wires with older thermostats. Luckily the in wall wiring has three wires. Any help to point out the C wire for my setup? Or ...
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5k views

Connected C-Wire to new Smart Thermostat and Furnace board and still no power

I need help. I've been surfing the internet and have had no luck finding answers to my situation so am hoping for some guidance. I've seen other questions here answered but none that suit my issue so ...
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1answer
134 views

How to connect c-wire to Burnham Series 2 boiler?

I am trying to install my ecobee 3 light but the previous thermostat did not use any c wire. Fortunately, there was an unused wire in the wall and I would like to set it up as a c-wire. The problem is ...
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1answer
1k views

Add-A-Wire - COMMON / C Wire to a 3 Wire Thermostat

I am battling a Nest and losing at every turn. I have a 2 zone system and was able to install a Nest on the 1st floor by repurposing a wire as a COMMON wire. Unfortunately, the 2nd floor only has 3 ...
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43 views

C-Wire identification

I am interested in replacing an older thermostat with a modern networked 'smart' thermostat \ humidity monitor. That being said, does the photographed thermostat have a C-wire? The thermostat ...
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137 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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1answer
2k views

Where to add C wire on this air handler?

Thanks for helping me here. I am adding a new wifi thermostat to my system but need to add a C wire directly to the air handler (system is a First Co air handler with hot water boiler for heat and ...
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1answer
42 views

Installing a Honeywell Wifi thermostat and need a C wire connection [duplicate]

My current thermostat is wired as follows and the wires are from my Separate heater and separate AC air handler: W - From my heat R - From my heat Rc - From my AC Handler Y - From the compressor G -...
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Using T-Terminal for C-Terminal on Lennox Furnace — Thermostat will not power

Furnace: Lennox Pulse Thermostat: Honeywell RTH6500WF I have the similar setup as the person in the below link Can I use the T terminal in my furnace as the C for a Wifi Thermostat? When I ...
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how to communicate thermostat to turn on wood heat system when during heat pump defrost cycle

I have physically disconnected the strip heaters in my air handler but the fan still runs which I do not want. I have a wood boiler I want to run in place of the aux heat Can I disconnect the white ...
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22 views

How should I wire my thermostat considering the existing adapter device?

Currently 18-4 is running from furnace to thermostat. I should be able just to use the T terminal to get power but there's some kind of funky adapter on it. Any know what the adapter is for and how ...
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50 views

Can I use an available wire as a C-wire by adding it to an unoccupied 24v terminal?

I want to add new thermostats in my home. Luckily, the wiring to my thermostat has an unused wire in the bundle for the required "C-Wire". It has R,G,Y,W, and an unused blue. The thermostat wiring ...
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1answer
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Can't find HVAC C terminal

Could any of these be the c terminal on my hvac unit? There's already a c wire there, just can't figure out where to connect it.
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Can I use the T terminal in my furnace as the C for a Wifi Thermostat?

I've read many posts on this, and believe I know what to do, but want to make sure. My furnace (a Lennox G14 Series) does not have a C terminal which needs to be connected to the C terminal in my new ...
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25 views

How should I connect a new Ecobee4 thermostat?

I'm wanting to hook a Ecobee4 thermostat up. On my furnace I have 5 terminals R with a red wire attached, W with a white wire attached, Y with 2 black wires attached, G with a green wire attached and ...
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33 views

Fan Blows Constantly Even With C Wire

Nest stated that my furnace only set up (we have an evap cooler) would work with their Nest E product. I self installed only two wires, R and W. The heating works; however, the fan always blows ...
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1answer
133 views

Zone Controller T-Stat Wiring w/ 24V transformer, isolation relays for 2 zones

I have a new Navien SmartZone+ 6-Zone Control for my boiler-based heating system. It is great, except it provides no power on C. I realize the internet has researched the heck out of adding a C ...
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164 views

Can I just extend this blue wire in furnace for Nest thermostat?

First time doing this, don't want to burn house down. The brown bundle is coming from thermostat, the white bundle I suspect is coming from A/C unit. Do I follow these steps? Find a scrap piece of 18 ...
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37 views

How to identify a c wire?

I have 3 wires coming out from the wall at my new house (red, white, blue). It is a water boiler heat only system. The tstat was already removed unfortunately. I thought the blue wire was the C wire, ...
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29 views

Four thermostats and three zone valves

I want to ask HVAC experts how to troubleshoot my floor heating system. I have a Lynx-85a boiler, pumping hot water into three zones, one per room and three zone valves. For some reason, original ...
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77 views

No C terminal on furnace

This old Lennox furnace has no c terminal. I can run a wire directly from the furnace to the thermostat. Question is, which terminal do I hook it to?
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68 views

Thermostat has two wires going into C terminal

Trying to help my dad install his new Nest thermostat - for some reason his thermostat has two wires going into the C terminal. I've searched and cannot find any other question about a setup like ...
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31 views

AC Common wire disappears

On my furnace there is a wire that is labeled C/Common. But at my thermostat there is no common wire. Wires on furnace control panel: W - White Y - Yellow G - Green C - Common Wires at my thermostat: ...