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

thermostat does not accept C wire connected to AC unit

I have three identical thermostats, model Radio Thermostat CT101. Two of them have C wires connected to the burner and work fine. The third one controls a heating zone and also central AC. It has R ...
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1answer
79 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 ...
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48 views

No 24VAC between R and C on Rudd R801 Control Board

I’m replacing a older programmable thermostat with Ecobee 4 which is to control a Ruud R801 HVAC unit installed last year. I have access at the thermostat to a wire (orange) that goes to the C ...
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1answer
136 views

Connect C wire to Furnace

I have a Lenox Merit system in the house. I am trying to install Nest E thermostats and want to do it with a C wire. I noticed an unused Blue Wire (pic attached) at the thermostat location and then in ...
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1answer
207 views

Where is the C wire terminal on my boiler

I am trying to connect the T5+ smart thermostat to my oil based furnace. I see there are only two used wires at the thermostat R And W but 3 additional cores available. My boiler is a old Weil McLain ...
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312 views

Where should I connect my C wire on Goodman GMP075-3 Rev.B

I am trying to install an ecobee4 to replace a digital battery powered thermostat. I removed the existing thermostat and found that there was a spare blue wire that was wrapped around the others that ...
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1answer
287 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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1answer
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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2answers
3k views

Where do I connect a C wire in an old Furnace?

I am hoping to be able to upgrade to a smart thermostat but unfortunately my furnace doesn't have the "easy" option with an obvious C terminal. My furnace is OLD but it actually has the full 5 ...
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1answer
93 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
116 views

How to identify the C terminal on my HVAC [duplicate]

As you can see I have a Y G W R/2 C/3 D/1 terminals on my HVAC. I am planning to change my thermostat to one that requires a c line. There are 2 spare lines available, however I am not sure which is ...
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1answer
976 views

Where to connect c wire in furnace?

I'm trying to figure out where to connect a C wire from a thermostat to my furnace. I found this old post for the same furnace type (Trane XE70), but it seems as though a red wire goes to the terminal ...
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833 views

Why does my Nest thermostat report error e195 when I try to use the air conditioning?

I had a Nest E installed in February and it has worked really well until it was time to turn on the AC. Now I get random e195 errors (no power detected to the R wire). The most likely answer from my ...
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3answers
171 views

Confirming C wire in my thermostat

can someone confirm that the blue wire is the "C wire"? What are the other wires (yellow, light pink, brown, and orange) that are not connected to anything?
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88 views

Why doesn't my thermostat work?

I replaced old thermostat with Honeywell wifi and added C wire from furnace to new thermostat. I left the jumper wire on Rc and R in place and wifi would not come on line. Checked C wire and have ...
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1answer
12k views

Nest thermostat not turning on heat

I have an old gas furnace/boiler for hot water baseboard heat and I'm trying to switch from a 2 wire mercury bulb thermostat to a Nest Thermostat "E" (the new white faced one). There are 5 wires in ...
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1answer
232 views

WiFi Thermostat - C Wire

I am trying to install an Ecobee 3 thermostat to replace the upstairs one I have now but the 3rd wire isn't connected to anything on either end. I added the basement thermostat just to complete the ...
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361 views

3 wire heating system, has 3 unused wires with 16v, can any be used as a common wire?

I hopefully have a quick question. I am thinking of getting a Ecobee or Nest smart thermostat, but doing my checks/research before getting one for this house. I rent, so I can only do minimal changes. ...
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1answer
247 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
409 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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0answers
204 views

Thermostat for my furnace has no power during fan-off delay?

I have an older Tempstar 5000 furnace and a newish Honeywell wifi thermostat. The furnace works fine and the thermostat appears to be wired correctly (4 wires including C wire) but for some reason, ...
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836 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
637 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
221 views

Red Wire labelled as 'Common' in HVAC

I'm looking to replace my old thermostat with a wifi one. Looking at the wiring on my HVAC, I can see red and white wires connected (matching what's connected to the back of the existing thermostat). ...
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296 views

Adding a C wire to thermostat with oil berner and AC

I have a oil burner for baseboard heat and forced air AC that is controlled by one thermostat. There are a total of 5 wires coming to the thermostat 2 wires from the boiler and 3 wires coming from the ...
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1answer
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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1answer
578 views

Wiring a C (common) wire to a Triangle Tube Prestige Excellence 110?

Wiring noob here. Can someone give me step-by-step instructions for where and how I should attach a C (common) wire to a Triangle Tube Prestige Excellence 110 boiler for a ecobee3 thermostat? I think ...
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328 views

Installing new thermostat without a C wire. Can I use my heater/R wire instead? Random 13V as well

I'm installing a thermostat, but I don't appear to have a C wire. My old thermostat had R/RH,Y,G,and W. It's an AC system that was setup before I got here. The actual AC unit is a long way away and ...
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597 views

Adding a C wire

I know this question has been asked multiple times and I'm going to try some of the methods I have read in other threads but wanted to ask this question since I didn't see anyone else's wired the way ...
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1answer
701 views

Honeywell VR8300A3500 Single Stage Heat Gas Valve to Ecobee3 with C wire

Hey everyone have a quick question regarding a honeywell VR8300A3500 Single Stage Heat Gas Valve and the introduction of a Ecobee3 wifi enabled thermostat with a "C" wire. just want to make sure i am ...
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857 views

Thermostat will not power on with C wire, but it has voltage

I recently purchased a Honeywell wifi thermostat and tried to hook it up as a replacement for an existing battery powered unit. I have a typical forced air HVAC setup with gas furnace (no heat pump), ...
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643 views

Honeywell WiFi thermostat newly installed--not working

I just replaced a 2 wire thermostat with a wifi one that required a c wire. There was an unused blue wire which I attached to the C connector on the transformer at the furnace. At the thermostat, the ...
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1answer
674 views

Need help adding a C wire for a wifi thermostat

With the increasing popularity of wifi thermostats I know this question has been asked many times, however I'll ask it again fr my specific situation. How do I add a "C" wire to my existing air ...
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1answer
587 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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1answer
513 views

Adding a C/Common wire to HVAC system

So I'm looking for some help in identifying where I can attach a C/Common Wire to my HVAC system, but unfortunately my system doesn't have a control board that I can easily attach a powerkit to. For ...
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420 views

How can I tell if C wire is active and connected to Thermostats?

We are trying to install a smart thermostat (Ecobee 3) so we are in need of a C wire from our boiler. We see a green wire in the wall, but it's not connected to our thermostat currently since it ...
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339 views

Wireless Transformer no C-Wire

I'm trying to install a wireless thermostat but i ran into issue putting in an external thermostat. I have a 2 Stage Cool / 1 Stage heat system. I have the Red 24V from Air Handler connected to R. I ...
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1answer
2k views

Where can I connect the C wire on the A/C side?

I’m trying to replace my thermostat with the Honeywell Smart-WiFi thermostat. Quick summary, I have an extra yellow wire which I’m making the C wire, but its not connected at the other end and I’m not ...
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1answer
2k views

How do I connect a C-wire on a Triangle Tube Prestige Solo 110? [duplicate]

I purchased a Honeywell RTH6580WF to use with my recently installed Triangle Tube Prestige Solo 110 propane boiler. I only have two wires at my existing heat-only thermostat. I understand that the c-...
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0answers
214 views

How can I add a common “C” wire to my thermostat? [duplicate]

Possible Duplicate: Options for adding “C” wire to thermostat I recently bought the Honeywell THM5320R Wireless thermostat. After going to hook it up I found what many others have, it requires a ...
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1answer
2k views

How to connect Nest in Europe

I found a question regarding the Nest thermostat here. But that is only a question "Will it work?". Thanks to that I know it WILL, the problem is...HOW. I know the wire naming conventions are ...
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1answer
2k views

Can a Ground Wire be attatched to a nail in wood stud?

Guilty as assumed: I've installed a thermostat connected to a single electric baseboard. Is it possible to connect the load and line ground wires to a nail which is attached to a wood stud? OR, simply ...
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2answers
33 views

Home thermostat woes

I tried to switch to a new smart thermostat in my home. When I was adding it, something happened. The new thermostat didn't show any power (And yes, the C wire was plugged in). Not knowing what else ...
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1answer
691 views

Can I buy a 24v transformer with a dedicated common c-wire feed?

I have an oil furnace that feeds hot water to baseboard in four zones in my house and also to a hot water tank for tap water. There is a 24vac transformer with two output wires that feed power to the ...
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2answers
2k views

Isolation relay for Ecobee smart thermostat: NC or NO?

I've been looking for "isolation relays" to install an Ecobee 3 smart thermostat on my 2-wire T/T furnace (replacing a Honeywell round thermostat). I know I want to use the 24VAC transformer/relay ...
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4answers
59 views

Wifi Thermostat, No C wire on HVAC unit. No control board? Condo

Looking to install Ecobee thermostat. Only 4 wires coming from unit. Ecoboo has power extender kit but there's no control board on the HVAC unit, so I can't locate a c wire. Any help would be ...
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1answer
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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4answers
14k views

How can I modify a 4 wire thermostat to a new thermostat requiring c wire?

I attempted to replace my thermostat with a fancy new Trane z-wave enabled model. To my dismay my home was only wired with a 4 wire setup with no 5 hidden in the bundle. I followed Insx on the web ...
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1answer
17k views

Wireless Thermostat C-Wire Substitute

I've read How can I add a "C" wire to my thermostat? and checked out the Venstar Add-A-Wire Accessory. I've watched Honeywell's YouTube video on "DIY Wi-Fi Thermostat Substitute G-Wire for C-Wire," ...
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1answer
48 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 ...