Skip to main content

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.

Filter by
Sorted by
Tagged with
0 votes
1 answer
66 views

Why does my Sensi thermostat shut down and reboot when calling for AC?

I have a Sensi smart touch thermostat. My home runs a dual transformer system with one 24v for heat and one 24v for cooling. I do not have any C wires for my thermostats. I jumped the G and Y wires at ...
Angelo's user avatar
  • 1
0 votes
0 answers
20 views

Installing an Ecobee 3 Lite PEK to my air conditioner with NO control board

I'm trying to install an Ecobee 3 Lite and upgrade the old thermostat. It's setup as air conditioning only. I do not have a C wire, only R, Y, and G so I need to install the PEK at the air ...
Will's user avatar
  • 1
0 votes
1 answer
72 views

External (C Wire) Power Supply Use for Cooling Only unit

Question regarding using an external 24V power supply to provide power to a smart/WiFi thermostat. I’m not clear on why both Honeywell and Emerson/Sensi docs state that the use of an external power ...
Paul's user avatar
  • 3
2 votes
1 answer
95 views

Need C-wire for new Honeywell RTH6500WF Thermostat

I am upgrading my old non-wifi programmable thermostats with Honeywell wifi models. These need a C-wire and my wiring only has 4 conductors and no C-wire (see image). I contacted Honeywell support and ...
NetGeni59's user avatar
0 votes
2 answers
36 views

Another C-wire for Nest thermostat question

Some background first. 30-ish year old furnace/boiler with a zone system and six zones. This was my parents full-time residence in rural Maine, but after my father passed away in 2022, and my mother ...
jsbigs's user avatar
  • 1
1 vote
1 answer
45 views

Where do I get a "C" common wire on Utica Boiler UH15B-060K

Here are some pictures. The thermostat currently has 2 wired, red and white. There's 3rd wire available that's not connected to anything, and not connected to the boiler anywhere either. And the ...
Paul's user avatar
  • 13
1 vote
1 answer
40 views

Nest Power Connector (C Wire) on A/C unit GMP075-4

I’m trying to use a Nest thermostat on my older Goodman GMP075-4 unit. I have a Y, R, W, and G connector for the thermostat. I’ve read through a few number of the other questions related to this on ...
ariagno's user avatar
  • 111
3 votes
3 answers
406 views

Connecting C-wire to 1989 Forced Air Electric Heater

Can anybody figure out where a C-wire would be connected in this old forced air electric furnace? How do you test it with a multimeter to make sure? Big 240V cables are at 1 (pink circle) in picture; ...
Persil Imberbe's user avatar
0 votes
0 answers
16 views

Honeywell rth9585wf to control Boiler and AC

I'd like to use a single Honeywell RTH9585WF (Smart Color Thermostat with Wifi) to control an existing radiator system (boiler) and existing Central air AC. Existing wiring: Boiler thermostat (first ...
Internet Tough Guy's user avatar
1 vote
1 answer
33 views

Furnace not starting after i added c wire connection

I just got a sensi lite system. My system didn't have c wire but once i connected c wire, the furnace is not even starting even if i set the temp to 90 degrees. Yesterday without. Connection i was ...
Scorpio84's user avatar
1 vote
1 answer
57 views

How can I connect C-wire at 2-wire Boiler side with existing 24v transformer?

Two zones/thermostats each with 3 wire cable running from boiler room. It appears only 2 of the wires are hooked up (Red and White). There is a 3rd unused and not-hooked-up wire that is dark blue, for ...
jflbball's user avatar
0 votes
0 answers
30 views

Honeywell T9 won't work on Trane System

I attached all the wires to the correct colors, but the thermostat would not power up. So I reinstalled the old basic thermostat and it worked. A few days later I looked at my photo of the wiring and ...
David G's user avatar
0 votes
0 answers
29 views

How do I wire a Goodman AUX Heat Kit?

I was installing a new thermostat and had to connect a C wire on a Goodman ARUF for up stairs. While in the attic I noticed the white wires were not connected and I do have a AUX Heat Kit installed. ...
Shawn Folsom's user avatar
0 votes
1 answer
116 views

Connecting Nest thermostat to this power adapter

My question is probably simple for those in the know. I've looked at the manual, and researched and Googled, however I'm still not confident. I tested this and got 24v on the red wire in bottom left ...
user182393's user avatar
0 votes
0 answers
77 views

How do I connect thermostat C-wire to Peerless boiler setup?

I’m having issues getting power to the thermostats over the C-wire. I have both an HVAC system and an oil burner (Peerless WBV -03 Boiler with a Hydrostat 3250-Plus control module). The oil burner ...
Jim's user avatar
  • 1
0 votes
0 answers
40 views

Where to connect c wire for thermostat to hydrostat 3250-plus

trying to add c wire for nest learning thermostat but there is no connection on the heater. Where can I connect?
Hannah's user avatar
  • 1
0 votes
1 answer
68 views

Where do I connect thermostat C-wire to the Peerless boiler relay panel?

I’m looking to replace my existing thermostats (two zones) with smart thermostats that require a C-wire. The current thermostats do not have the C-wire connected, but the wire is already present in ...
Jim's user avatar
  • 1
0 votes
0 answers
31 views

Need to have smart thermostat wiring explained like I am 5

So, I have finally purchased my first house, and one of the first things I wanted to upgrade is the thermostat. The heater is ancient, and still works, as well as the a/c. Outside of a now utter lack ...
Aaron Gray's user avatar
0 votes
0 answers
44 views

New Honeywell thermostat doesn't work

I'm a newbie, and I have a question. My old thermostat is broken, and the fan keeps running and cannot be turned off, but everything else is fine. So, I replaced it with a new Honeywell RTH8800WF ...
Daniel's user avatar
  • 1
-1 votes
1 answer
35 views

Common terminal question on old furnace and air conditioner with new smart thermostat

Trying to solve an odd problem with my T5 Lyric smart thermostat and an old furnace/AC. I'll try and be concise. The model of furnace is: Goodman, GMP075-4 Rev B Details, and photos below for help: ...
thegreataus's user avatar
1 vote
1 answer
844 views

Installing a thermostat with 3 wires only (red/R, white/W, and black/G)

I want to connect an Ecobee to my house, under the constraints imposed at the thermostat (pictured below); you will immediately note that there is no yellow/Y wire (because there is no air-...
Nima Talebi's user avatar
0 votes
1 answer
67 views

Is there any chance of a problem using C terminal on furnace to wire a new smart thermostat?

Bought a house built in 1995 with I believe original Ruud Silhouette II gas furnace, central A/C, and a Maple Chase 9600 thermostat powered by two AA batteries. Upgrading to an Ecobee smart ...
user1441998's user avatar
0 votes
2 answers
102 views

Is the "C" wire here tied to ground?

Looking at this diagram, it looks like the "C" wire for a thermostat, marked as "COM" on some intermediate component my garage heater, is actually also tied to the ground of the ...
pioto's user avatar
  • 153
2 votes
1 answer
123 views

Where do I attach C-Wire in this Rheem RBHA-24J11NUBAI system

I'm installing an ecobee lite thermostat to this system and the c (blue) wire was hidden inside the wall, tracing the c wire inside the air handler I see that is not connected. I have tried connecting ...
Damian H's user avatar
0 votes
3 answers
166 views

Installing smart thermostat but can’t fish new wire

Forgive my lack of knowledge here. I bought my husband an Amazon smart thermostat awhile back so that it would go with all of our other Alexa smart home stuff. We hooked it up where the previous (...
Lydnort 's user avatar
2 votes
1 answer
140 views

DUAL Nest Power Connector wiring - separate heat/cool thermostats

My house has separate thermostats for heat and cool, each located in a different part of the house. It's a single-zone forced air system handling both heat and cool. The existing thermostat wiring ...
DougSlug's user avatar
1 vote
1 answer
83 views

How to add a C wire to a lennox G8-137 wd-64280-L5

I have a Lennox G8-137 WD-64280-L5 furnace. I am trying to update the wiring going to the thermostat due to it being cloth covered, and I also plan to put in a google nest thermostat. Where is my C ...
Lloyd's user avatar
  • 13
0 votes
1 answer
1k views

How does a Google Nest power connector work?

I am looking at the installation instructions and they all show that the power connector goes back to the furnace/AC control panelIf this is installed just to make sure the thermostat gets enough ...
MiniMe's user avatar
  • 3,422
0 votes
0 answers
207 views

Adding smart thermostat (nest) to burnham series 2 boiler

I’m trying to add a nest thermostat to my burnham series 2 boiler with two zones. My original thermostat has a red and white wire going to W and R with a jumper from R to RC. See first photo. Where ...
Reed1099's user avatar
1 vote
2 answers
121 views

Nest thermostat and no C wire at my boiler

so I bought a nest thermostat and it keeps running through the AAA batteries, recommending that I use a C wire, though there's just 2 coming out of the wall (red and white). I got C wire/power adapter ...
Brian Battenfeld's user avatar
0 votes
1 answer
85 views

No C terminal, where to tie in smart thermostat

Trying to figure out how to connect the Ecobee adapter. I can follow up with more pics and info / questions (like connecting via the transformer), but everything I’ve read up on has led me to this ...
Babyaligators's user avatar
0 votes
0 answers
28 views

C-Wire for L8148J Thermostat

Thanks for very informative videos. Where do I connect C wire on the 8148J Aquastat to get 24 v for the Nest thermostat? Thanks
Peter Deebrah's user avatar
1 vote
0 answers
35 views

Installing c-wire adapter on hvac

I'm installing an Amazon smart thermostat. The hvac control board has 3 of the wires that the instructions state to disconnect and connect to the adapter (G, W, Y). But it's missing R, and Y has two ...
Ctakacs9's user avatar
2 votes
1 answer
263 views

Where to connect a common wire to a Burnham alpine Furnace

Like many on this site I am trying to install a smart thermostat. I have 3 wires, 24V Red, white, and blue at the thermostat, but only 2 down at the boiler. My boiler is a Burnham Alpine model number ...
Paul's user avatar
  • 21
0 votes
0 answers
37 views

Where does my C Wire go?

Changing thermostat and need to connect c wire at furnace. I connected to the brown bundle based on the wiring diagram and it worked to get power to the new thermostat. However, only the the fan runs ...
Morgan's user avatar
  • 1
0 votes
1 answer
69 views

How can I install an Ecobee with no C-wire and no panel in the air handler? [closed]

I am looking to install an Ecobee but I have reached a C wire issue. Ecobee support didn't think it would be possible without adding another wire but they didn't have the schematic. I am just ...
Castle50's user avatar
1 vote
0 answers
154 views

Y wire question: Help to connect smart thermostat with C wire adaptor

Trying to install an amazon smart thermostat with a c wire adaptor. On the thermostat end, pretty straight forward. Rh, W, Y, G wires. Noted that a blue colored wire is Y wire. SEE PICTURE When I went ...
George's user avatar
  • 11
0 votes
2 answers
173 views

How to connect my C wire (blue) to the transformer? HVAC

Trying to connect my smart thermostat up, but the C wire (blue wire) is not connected to anything, it’s just there capped off . (Bottom left) Anyone know where I should connect the blue wire to so it ...
Theman81's user avatar
2 votes
3 answers
1k views

How can I get power to my new Ecobee thermostat?

I purchased a new Ecobee smart thermostat which requires a C wire (the Nest unit did not) to power the thermostat. I located the blue C wire behind the thermostat, but it was not connected on the ...
Nathan's user avatar
  • 21
0 votes
2 answers
118 views

Do I have a wire to repurpose as a C-wire?

Do I have a wire to repurpose as a C-wire??
Tracy Evans's user avatar
-1 votes
1 answer
44 views

Where to add C-Wire connection for thermostat

I’d like to ask a follow up question on this thread below. How can I add a "C" common wire to this system? This was the fix: In the wiring diagram in the PDF you linked, the BR (brown) wire ...
user172250's user avatar
0 votes
1 answer
150 views

Do I have a C wire (or something I can repurpose)?

Pretty old looking thermostat, but the house itself isn't that old (I think 1997). There's no terminal with a "C" at all here, but there's 6 wires including a "blue one" which this ...
Steve N's user avatar
  • 101
3 votes
1 answer
946 views

Finding the 24V C-wire from Carrier AC blower to connect to a Smart Thermostat

I want to install a Smart Thermostat to control my AC unit. The current "dumb" thermostat is battery powered and does not use a C-wire (see current thermostat wiring pic). When I look at the ...
Steve Bell's user avatar
1 vote
2 answers
140 views

How to make c-wire to a new boiler using Fast-Stat common maker?

I'm seeking assistance regarding connecting a C-wire (for Ecobee) to a new boiler using the Fast-Stat common maker. The new boiler currently has two thermostat wires available for connection. However, ...
Kamsu's user avatar
  • 113
1 vote
3 answers
129 views

Old furnace no C terminal

I’m trying to install a smart thermostat and my furnace does not have a C terminal. The thermostat has an unused blue wire, and I connected it to what I thought was a common, but the unit is not ...
bperham's user avatar
  • 11
1 vote
0 answers
217 views

Y wire on thermostat connected to C on furnace

I have a very similar problem to the question Why is Thermostat Y wire connected to C terminal on furnace? . The big difference is that I dont have an "extra wire" to use. Only 4 wires go to ...
Javier Martin's user avatar
0 votes
1 answer
129 views

Old house, want to update thermostat

I bought an older house (1897!) and am slowly but surely going around and repairing things and updating them. I want to update my thermostat to an ecobee one. We only have radiators and no AC, but ...
Brian Desmond's user avatar
1 vote
1 answer
444 views

Adding a C wire to an Intertherm system

I am trying to add an Ecobee smart thermostat to an older Intertherm furnace and A/C. I have extra wires running to my thermostat, but can't figure out what to connect to in the furnace wiring. Any ...
oldKickstart's user avatar
-1 votes
1 answer
82 views

Can’t find C Terminal Burnham Series ES2

Try to install Nest thermostat 3rd gen. I have 3 wires coming from the furnace: R, W, and G. I connected them to Nest pretty simple there, but low battery, Wi-Fi not working on a daily basis. There is ...
Mike's user avatar
  • 1
0 votes
1 answer
234 views

Where's the c-wire on my air conditioner?

I'm trying to install a smart thermostat in my home. It has only an external air conditioner (model P3RD-042K, here's the manual/wiring diagrams), no heat. The current thermostat has an unused blue ...
Rafael's user avatar
  • 197

1
2 3 4 5
12