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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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157 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
165 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
2k 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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1answer
569 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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1answer
21 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 ...
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1answer
384 views

Old AC and Gas Boiler wiring for new thermostat

I need help connecting a new 'C' wire for a Honeywell RTH6500WF thermostat. As you can see the heating is an old boilder with a simple pump to circulate the hot water to the baseboard radiators. The ...
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1answer
961 views

How can I add a C-wire to a Venstar T5800 thermostat?

I am trying to replace my existing thermostat. My old thermostat has: Rh, W (coming from the heating unit). Rc, Y, G (coming from the AC unit). On the Venstar T5800, I can map as follows: Rh+Rc -...
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803 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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1answer
226 views

C Wire placement in HVAC?

I'm installing a new thermostat and the previous one did not have a C wire connected. Tracing in back to the HVAC, I can't see a C output connection? Based on the wiring diagram (and reading other ...
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1answer
69 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
121 views

Connect Wifi Thermostat to Goodman GMP050-3?

I'm trying to connect up a wifi thermostat to Goodman furnace, specifically the GMP050-3. I've done some reading on this but I'm still not quite sure how to go about it. Specifically, I'm not sure ...
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1answer
575 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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2answers
43 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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1answer
73 views

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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1answer
34 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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2answers
62 views

How can I install a Honeywell Wifi RTH6580WF1001 thermostat in place of a Honeywell RTH2300b?

I have separate heating (hot water) and air handler (cooling System). The current thermostat I'm using is a Honeywell RTH2300B and the new one I want to install is a Honeywell Wifi RTH6580WF1001. The ...
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1answer
23 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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1answer
33 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 ...
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24 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 ...
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1answer
35 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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1answer
23 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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1answer
83 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 ...
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1answer
84 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 ...
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0answers
18 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: ...
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1answer
43 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
56 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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1answer
42 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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2answers
877 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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1answer
34 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 ...
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7answers
493k views

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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1answer
3k views

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
48 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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0answers
99 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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2answers
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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0answers
17 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 ...
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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 ...
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1answer
27 views

C wire in wireless Thermostat Transofrmer question

I have a rheem handler with a 46-23115-02 transformer. I do not have a C-wire connection that I can see. I have a 5 wire cable... so I do have a blue wire available that I can connect as the common ...
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0answers
29 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 ...
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2answers
54 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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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 ...
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8answers
55k 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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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 ...
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1answer
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
68 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
24k views

How many wires can be connected to the C terminal at the furnace?

I'd like install a new Wi-Fi thermostat. The old one didn't have a C-wire but luckily there is an unused wire on both sides (one coming out of the wall and one at the furnace not connected yet), so I ...
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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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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 ...
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0answers
91 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
42 views

“C” wire on thermostat

I have an electric furnace that has power, fan, electric heat, but I do not have a "C" wire. The thermostat wiring has several unused wires that are routed to furnace. It is a matter of applying ...
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1answer
71 views

Smart Thermostat without C on Heater

I want to hook up my Honeywell rth9580wf to a natural gas garage heater that only has R, W, and G (not in use). It's currently hooked up to a standard battery powered Honeywell thermostat. I've read ...