Stack Exchange Network

Stack Exchange network consists of 175 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

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.

1
vote
1answer
16 views

Identifying C wire

thank you in advance. I have been struggling to find a proper way to install my ecobee. It is again 'C wire' issue. My old thermostat uses 4 wires (red, yellow, green, white) and does not use c wire. ...
3
votes
3answers
861 views

How many wires should be in a new thermostat cable?

When roughing in thermostat wire, how many pair wire would you use to cover most thermostats? I'm asking because keep seeing questions about C wire and wifi.
0
votes
0answers
19 views

Where to install C wire?

I need to run new thermostat wire since I don't have a C wire to power my smart thermostat, but need some guidance on where to hook it up. I have five wires at my thermostat, two going back to my ...
1
vote
2answers
47 views

I have an unused C wire hooked up to thermostat and have no idea where to connect it to the furnace for power

I know this question gets asked all the time but I've spent hours staring at forums as well as my furnace and at this point I'm desperate. I just bought a nest thermostat that needs a C wire ...
1
vote
1answer
18 views

Old furnace with extra wire, but no c terminal Janitrol, 19 year old furnace

I've searched multiple threads regarding this, but I didn't manage to find any that seemed to match my use case. My board doesnt have a C terminal, and it doesn't have the other terminals connect to ...
3
votes
0answers
41 views

Can I use this White Wire for a thermostat C wire?

An AC-only machine cools a storage facility: no heat. The 30 year old thermostat is to be replaced with a wifi thermostat, which requires a C-wire to power the electronics. There are 4 wires: Red (...
1
vote
1answer
28 views

Furnace with no “C” connection

I have a mobile home furnace. This furnace only has a 4 wire connection terminal, G,W,R,Y. I also have a condensing unit outside with the 24 volt 2 wires coming to the furnace. I know I connect one to ...
1
vote
1answer
58 views

How to connect a new C wire

I have a 2 zone, single stage, heat only system with 2 wires running to each thermostat. I'm looking to install 2 Ecobee's; I have a second Honeywell AT72D1683 that I can install if needed and have ...
0
votes
0answers
56 views

Thermostat Wiring. 2 wires connecting to Y terminal

Did some more findings at furnace level (see furnace board image). The furnace board Y, W, G, and R terminals, ALL have a pair (2) of wires connected to them, instead of a single wire, making it a ...
1
vote
1answer
31 views

C Wire in Air Handler

Can someone please help me find where to connect a C wire for my smart thermostat? Here are some pictures with descriptions. It is difficult to get to the 24v connection in the back. My schematic ...
2
votes
2answers
50 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 ...
0
votes
0answers
31 views

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 ...
1
vote
1answer
53 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 ...
0
votes
1answer
24 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 ...
2
votes
1answer
48 views

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 ...
1
vote
1answer
76 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 ...
1
vote
1answer
52 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 ...
0
votes
0answers
19 views

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: ...
1
vote
1answer
69 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. ...
1
vote
1answer
62 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 ...
0
votes
1answer
43 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....
1
vote
1answer
24 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...
2
votes
1answer
56 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 ...
0
votes
0answers
18 views

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 ...
0
votes
1answer
30 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 ...
1
vote
0answers
33 views

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 ...
-2
votes
2answers
68 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 ...
0
votes
0answers
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 ...
0
votes
1answer
141 views

C wire - thermostat - not providing power

I'm replacing my old Honeywell thermostat with a new Wifi thermostat. My old/current one is battery powered and doesn't use the C wire. I found the C wire behind the plate. I connected the c wire to ...
2
votes
0answers
118 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, ...
0
votes
0answers
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 ...
1
vote
1answer
86 views

Can't get wifi thermostat to work with gas boiler

I bought a Sensi WiFi thermostat and I have been trying to install it. I can't quite figure out how this wiring should work. Here is a link to pictures of the boiler and the current thermostat. The ...
1
vote
1answer
81 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 ...
1
vote
0answers
110 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 ...
1
vote
1answer
35 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 ...
0
votes
1answer
40 views

how to connect C wire for ecobee lite to Weil-McLain EG Series-5 gas steam boiler

I want to upgrade from a battery powered Honeywell thermostat to an ecobee3 lite. This is for heat only. My current Honeywell has two wires: Red and White. Missing is the C cable. There are enough ...
1
vote
1answer
40 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 -...
0
votes
0answers
89 views

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 ...
0
votes
0answers
15 views

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 ...
0
votes
0answers
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 ...
1
vote
0answers
45 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 ...
3
votes
1answer
40 views

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.
1
vote
0answers
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 ...
0
votes
0answers
26 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 ...
1
vote
1answer
88 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 ...
1
vote
1answer
85 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 ...
0
votes
0answers
35 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, ...
0
votes
0answers
27 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 ...
0
votes
0answers
35 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?
1
vote
0answers
42 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 ...