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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803 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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34 views

Ecobee 3 - I have 3 Wires

I have three wires coming to the existing, very old, thermostat: Black, but wired to the "R" terminal of the current thermostat. White, but wired to the "W" terminal of the ...
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1k views

C wire and smart thermostat

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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199 views

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

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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99 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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49 views

Can I pull a c-wire from a second nearby thermostat?

I have a thermostat that controls the AC/Heat upstairs which is located on my bedroom wall. Right below that I have another Millivolt thermostat for the gas fireplace in my bedroom. If I want to ...
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760 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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127 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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155 views

Replace thermostat wiring from my Carrier Weathermaker 8000 to my Nest thermostat

I'd like to replace the wiring from my Carrier Weathermaker 8000 to my thermostat to add a C wire. I assume I need to turn off the Carrier first, but there is no power switch that I can see on the ...
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17 views

Where Can I connect my C-wire on A Hot Water (Hydronic) Heating System?

I have a hydronic heating system (Lochnivar)that came controlled with an older (dumb) thermostat. I have 5 wires behind the wall and 5 wire in the wire packet going into heating system however only ...
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76 views

Can a C wire be used for two thermostats?

A friend of mine wants to upgrade his thermostats to WiFi thermostats but the thermostat wires ran to the thermostats are missing the C wire. There are 2 thermostat cables running from 2 units to 2 ...
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21 views

Adding C Wire as simple as C to C?

Short version: I ran a new 2-strand wire from my thermostat to the furnace/air handler unit to provide spare wires since the existing 5 wires are used up and I need a C. Is hooking up the C wire as ...
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143 views

Honeywell RTH9585WF Thermostat wiring question

My old thermostat LUXPRO TX 9600tsa uses 4 wires: W white G green R red hooked to RH and looped to RC and Y yellow This thing is not working right, so I purchased a Honeywell RTH9585WF WiFi ...
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39 views

Wiring Ecobee thermostat to Vulkan gas furnace with no C terminal

I am trying to wire up an Ecobee thermostat to an old (1997) Gas central heating system but I got up into the roof then realised I have no terminal labelled C. Now, I don't super know what I am doing, ...
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87 views

Installing a Nest thermostat without a C wire?

I am attempting to install a nest but do not have a common wire on my hvac unit, perhaps it is slightly dated. I have read that on older units the O terminal is the same as C and I can remove the ...
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771 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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974 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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1k 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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11k 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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860 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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234 views

Where to connect a C wire for my smart thermostat

I am trying to connect the c wire but I'm at a crossroads of sorts. I have a dual zone so there are 2 thermostat wires come into what looks like a relay box ( see pictures) I have located the ...
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1answer
235 views

Need help with wiring to thermostat and condensate pump

I've searched a lot and can't quite find what how to solve this one. I installed an ecobee smart thermostat, which didn't work with 5 wire connection so I switched to their PEK module with only 4 ...
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56 views

Does this seem like the right place to tap a C-Wire from my heater?

I need a C-wire for my thermostat but my heater only has R and W connectors (red circle). On the schematic on the heater, up top (red arrow), looks like: 5 is 24V Gnd (bit hard to read but i've ...
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80 views

Where to connect C wire if no C terminal

Hi wanting to connect Nest and want to install a C wire. HVAC only appears to have G,W,R so not sure where to connect C.
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239 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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106 views

How does this wiring work?

I have a Trane XV90 and XL 14i. The wiring looks a little strange as in the picture bellow. _____________ | | BK W2 W1 R G Y B/C YLO O |___||...
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953 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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4k 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
593 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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6k 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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990 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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295 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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772 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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648 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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173 views

C-Wire for a Vulcan Gas Central Heater for Nest Thermostat-E

I'm hoping the friendly people here could help me. I'm looking to purchase a Nest Thermostat-E but my current thermostat (Vulcan/Bonaire Summer Breeze) only has 2 black wires connected. I've searched ...
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43 views

Honeywell C wire on a dual transformer system

Currently I have dual transformer system From heat >> RH & W1 From cool >> Y1, Rc, G Honeywell provides a C wire adapter and also mentioned turning an unused wire into a C-wire. I do ...
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197 views

How do I add a “c” wire to the boiler for a Nest thermostat?

I have a Lennox wall mounted boiler (gwm 075ie), I am trying to connect a "c" wire so I can install nest thermostats. I have 3 zones, currently running 2 wires (r&w). There is an extra ...
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263 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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91 views

Where to connect C Wire to1990 Weil Mclain Steam Boiler

I am attempting to run a new 18/5 line in order to hook up an Ecobee 4 to my Weil Mclain boiler, as my current thermostat only has a R & W wire. I am having trouble figuring out where exactly to ...
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76 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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How to connect nest thermostat e for American standard heat pump 2005

current wining We have a 2005 heat pump. I tried b wire to nest C wire but it is not working
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746 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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2answers
293 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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24 views

how to add c wire to heat pump ac unit (only have wires with nuts)

I can’t figure out which is the C wire or how to make a C wire and how to connect it to my ecobee 3lite Power extender kit. My old thermostat has wires G,Y,RH, W/E, and O/B plugged in. No "C"...
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Is this wiring dangerous? Smart Thermostat C-wire AC adapter twisted together

Is this wiring scenario dangerous? Is it likely produce sparks or damage my HVAC system? Please read the description and see the image below. Description I didn't have a C-wire for my Emerson Sensi ...
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3k 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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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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291 views

Where should I connect my C-wire on my old Goodman unit (GMP075-4 rev 13)

I want see if someone help me on hooking up this new Honeywell thermostat with Wifi I just purchased. I have an old ac unit and I only have 3 connections to my circuit board which does not have an ...
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520 views

Where to add a c-wire on my Goodman furnace?

I'm looking to upgrade my old thermostat and need to run a c-wire. Where would be the best place to tap into?
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Connection for C wire on Mastertrol Mark V zone control panel

I have spent hours searching the web for information on this 20+ year old zone control panel, which supports 3 zones of Heat and A/C. The thermostat I'm replacing (on Zone 3) connects to T4/T5/T6 as ...

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