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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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can I use an unused y2 or w2 aux wire and connect to the C terminal

I got a new ecobee thermostat that requires a c wire. my current thermostat has 4 wires plugged in, and there are 2 extra wires not being used coming out of the wall one blue labled y2, and a brown ...
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1answer
156 views

Adding a C wire to older 3 wire

How do I use the green wire as a C wire as suggested in most installation instructions for the newer wi-fi thermostats? They all reference terminal strips at the furnace, all I have is the 3 wire ...
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2answers
912 views

Can I use the Y wire in place of the C wire for my new thermostat?

I'm looking to wire a Honeywell Lyric T5 to my furnace (I do not have an air conditioner, I do have a humidistat). My current wiring at the thermostat is G,W,Y,R. At the furnace it's G,R,C, and 2 at W,...
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84 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
122 views

Can I use the extra thermostat cable as C cable for wifi?

I just purchased an ecobee4 and I found that I need C wire for wifi which is not connected to my current thermostat. However, there 2 extra wires I found in the wall. Could you use one of them for the ...
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2k views

How do I connect the spare C wire to the old Lennox system (model # lennox g12q4-110)?

I am trying to install my Ecobee3 now. After finishing the connections, Ecobee did not power up. I did some reading and I believe the C-wire, though it is available is not connected to the power at ...
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1answer
11k 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
189 views

Where to connect c wire

I’m installing a new WiFi thermostat that needs the c wire. I ended up running new thermostat wires that contained the common wire but now I’m stuck on where to connect it to the furnace. Can ...
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1answer
446 views

C Wire for Thermostat

I am upgrading my thermostat (Have AC & Heat) and found that it doesn't have the "C" wire that I need to power my new thermostat. The furnace does have a terminal for C, but only condensation pump ...
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3answers
2k views

How do i hook up a new 5 wire cable to an existing 4 wire furnace

I would like to replace the existing thermostat wires on my 2000's era janitorial furnace with the upgraded 5 wire setup that will allow fan control of my Honeywell wifi 9000 thermostat. I was going ...
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3answers
324 views

Can I add a “C-Wire” to boiler with this device?

https://www.amazon.com/FAST-STAT-Common-Thermostat-Extender-Connection/dp/B01N6ERM04/ref=pd_sim_60_4?_encoding=UTF8&psc=1&refRID=D3D121DG0B4379V2TRC6 On the surface it appears that it will ...
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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
227 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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0answers
625 views

Honeywell WiFi thermostat jumper loop separate ac and gas furnace

I need to validate my understanding for the installation of a WiFi thermostat that requires 24volt continuous power to operate in a constant state. I am DIYer who is computer literate. Like a number ...
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326 views

NEST thermostat for hydronic floor heating: the three wire setup

I'm trying to install a 2nd generation Nest thermostat for my hydronic floors. So it's only meant for heating and not for cooling. Someone else removed the old thermostat a long time ago so I don't ...
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2answers
422 views

Max Current Supplied by Thermostat Wire

So I want to run a Raspberry Pi 3 off of thermostat wire. My question is, will the thermostat wire supply enough current for the raspberry pi (2.5 amps)?
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2answers
298 views

C wire thermostat assistance

I am trying to install a new wifi stat. The wiring seems to all be there but apparently not connected correctly. So far I have tried using the green wire from the furnace, the blue and the white from ...
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1answer
669 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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0answers
349 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
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
3k views

Where to connect c wire in furnace

I have 5 wires running to the thermostat from the furnace. The blue wire is not connected on either side. I'd like to connect it as my c wire for a smart thermostat. On the furnace I see W R Y G and ...
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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
196 views

Unsure where to find “C” connection on furnace

Another "don't have a C wire for thermostat" question. Been following along, and if I could identify the C connection at the furnace, I'd be all set. Unfortunately, it's not simply marked C or common. ...
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93 views

Smart Thermostat Wiring

All, First-time homeowner here. I recently bought a WiFi enabled thermostat which requires a C wire. My old unit did not need this, but I did have the extra wire in my wall to hook up to the unit. ...
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0answers
196 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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2answers
262 views

I have older HVAC unit (heat pump) and looking for the C wire to hook up to Smart Thermostat

I spent 2 hours with Thermostat vendor, Ecobee and they couldn't help me. I have R,G,Y,B and the white lead is not connected. I need some guidance on how to get a Common wire. I tested voltage and R-G,...
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1answer
84 views

Setting up an ecobee and need to adjust HVAC wiring

My HVAC control board has two bundles of wires. One has 5 wires which runs to the thermostat but the 5th wire which I want to use as C is currently unused. The second set runs to the unit outside (...
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1answer
278 views

Connect C wire Lennox G16

I bought a new thermostat that needs the c wire. Old thermostat wasnt using the blue c and was stuffed back in the wall. Come to find out the blue c wire is not connected to the furnace. Trying to ...
2
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1answer
155 views

How should I hook up my WiFi thermostat given my current wiring situation?

I've upgraded a few thermostats before, and they have been quite straightforward; i.e. take pictures and connect the wires as the the original. However, this is my first attempt at a "smart" WiFi-...
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1answer
727 views

Needing Help with new thermostat install (C Wire)

I am in the process of installing a new thermostat that requires a c wire. I checked my thermostat to see if it has a c wire running to it and it does not. After doing lots of googling and watching ...
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1answer
1k views

Adding a C (common) wire to my Goodman (Janitrol) furnace

I have a Goodman Janitrol furnace and I am needing to add a C (common) wire, for the newer thermostats. I would like to avoid the substituting G for C, and just run an additional wire. I have read ...
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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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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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0answers
60 views

Need c wire from Team air handler

Help- I have a new wifi thermostat and need to run c wire to unit from the air handler . There are a bunch of wires but no labels . I reviewed the wiring diagram and looks like the blue wire (way left ...
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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
195 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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2answers
834 views

Where to connect C-wire on old furnace (diagram attached)

I've got an old steam furnace and would like to add a common wire. The wire is already ran, I just have no idea where to connect it. I thought it would go to TR but that didn't work. Thanks in ...
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2answers
192 views

Lennox G16Q3-50 Furnace with AC, Door Interlock Switch and Main Circuit Breaker

If the door of the Lennox G16 is removed, thus the door interlock switch unpressed and system off. Does this mean that I only need to shut off the AC power from the outside breaker panel and leave the ...
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0answers
325 views

Help me to find C wire on A/C side

I replaced my old AC only thermostat with Honeywell RTH6580WF smart Thermostat. Also replaced existing 3 terminal wire with 4 for C wire hookup. TSTAT specs h t t p yourhome.honeywell.com/en/products/...
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2answers
8k views

Can't get the AC compressor to turn on after switching to Lyric T5 Thermostat

I swapped out my old thermostat with a Lyric T5 around Christmas time. I live in an older house so wasn't sure I could make it work. I opened my old thermostat and saw that there was a blue wire ...
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0answers
288 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
439 views

Install Common Wire (unable to find terminal or 24 VAC)

I bought a Nest 3rd Generation Thermostat. Live in a 2 family home, where my floor/basement has the boiler room/furnace. I have a Laars Mini Therm Furnace Model JVT. There's a thermostat upstairs as ...
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1answer
621 views

Thermostat wiring with external transformer

So I am trying to wire a Honeywell lyric thermostat and I tried following videos but got a little stuck. So I have wires R, W ,Y , G coming to my original thermostat. I bought an 24V external ...
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1answer
414 views

Pull 7- or 8-conductor thermostat cable?

I've got 4-conductor cable now, but am looking to put in a smart thermostat (ecobee3). It requires a C wire, or the use of their adapter kit, so I'm thinking of just pulling new cable. 7-conductor ...
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2answers
2k views

“C” wire in wall! Where does it go in air handler/furnace?

Got a wifi thermostat. Behind the old thermostat was a blue "C" wire. The other side of the blue wire in the equipment room isn't plugged into anything. I need to get the 24v common hooked up to this ...
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1answer
281 views

How do a replace an old baseboard thermostat with a wifi thermostat?

I don't know if this is a dual pole or single pole thermostat (n00b here, don't know what I'm talking about). I don't even know what voltage this is (240 or 120). But here's a photo of the wiring: ...
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1answer
2k views

Can I use a separate 24V transformer with an Ecobee 3 and an Aube relay?

I've purchased an Ecobee 3 Lite smart thermostat which requires 3.5 VA to operate but I'm using an Aube RC840T-240 electric heating relay with 24 V transformer which only provides 1.2 VA. Can I ...
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1answer
317 views

Help me to find C wire

GV1 - ZONE 1 VALVE GV2 - ZONE 2 VALVE Y1 - YELLOW WIRE 1 Y2 - YELLOW WIRE 2 R1 - RED WIRE 1 R2- RED WIRE 2 TT1 - ZONE 1 THERMOSTAT TT2 - ZONE 2 THERMOSTAT R RED WIRE W WHITE WIRE B BLUE WIRE BOILER ...
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1answer
361 views

Connect Ecobee3 thermostat - no c wire but c terminal occupied

I am trying to install a new Ecobee3 wi-fi thermostat to replace my old mercury thermostat. When I pull off old thermostat there are only 4 wires (red, white, yellow, green and a blue tied around). ...
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1answer
1k views

Add c wire to furnace for smart thermostat

I have an older furnace and am looking to add a c wire for a smart thermostat. Currently behind my thermostat I have red/black wire, however, there are 3 additional wires that are not connected. At ...