Questions tagged [thermostat]

Mechanical or electrical device used to control a heating, ventilation, and air conditioning (HVAC) system, or other temperature reliant system.

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2answers
807 views

Installing thermostat - No C wire or C terminal available on furnace

So I've looked through many posts all over reddit and other websites but it seems every furnace is slightly different. I am an early twenties guy who doesn't want to burn down his apartment. If ...
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14k views

why does my heat pump wiring diagram show 7 wires going to the thermostat but the thermostat only says it needs 5?

Here is a link to the wiring diagram for my heat pump. The thermostat that I am planning on buying has the following terminals C, G, Y, O/B, RC, R, Aux, E, and L. The instructions say to jump the RC ...
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2answers
74 views

Need a common wire

So, I recently moved. In my old place, I used my Nest without a common wire and never had an issue. However, in my new place, my Nest thermostat was working fine for about 20 days and started losing ...
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1answer
42 views

Try to rewire Nest and Furnace but Y is not used on Furnace

I installed a Nest at home and it worked OK. Recently, I noticed there was a power issue. Google and others suggested adding a power supply by using the existing G wire because there are only 4 wires. ...
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1answer
2k views

Hooking a wifi thermostat to a 2 wire boiler

I'm in the process of figuring out how to swap my existing thermostat for a new WiFi thermostat. Naturally it's connected to my home's boiler by 2 really old cloth wrapped wires. Examening the wires,...
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2answers
27 views

Thermostat settings two hvac units older house

So I purchased a historic house built in 1920. The house has two HVAC units, one for the upper floor, one for the lower. Total sq ft 3300. I had been setting the upstairs thermostat at about 83 ...
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1answer
174 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
746 views

How to install a 4-wire a/c & fan thermostat with only 3 wires

My home currently has a central a/c unit which is controlled from an 3-wire old mercury switch thermostat. I want to replace it with a newer Honeywell that requires 4 wires. The existing thermostat ...
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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
638 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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24 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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1answer
226 views

Old Thermostat with just R and Y wires?

UPDATE: this may be R and V, not R and Y, although I'm still not sure how it was set up. I am replacing an old thermostat in my house (the house is from the 60s, I'm not sure how old the thermostat ...
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141 views

Smart Thermostat and 24 volt transformer direct to thermostat

I have a hot water boiler and separate AC system and bought a wifi smart honeywell thermostat to get a C wire- installed a 24 volt transformer that has two wires if one goes to the C where should the ...
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3answers
29k views

Correct Wiring for Furnace Blower Motor

After getting my furnace blower motor replaced, it now runs only in the following scenarios: 1. Mode "Cool" Fan "Auto" 2. Mode "Cool" Fan "On" 3. Mode "Heat" Fan "On" In other words it will not run ...
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1answer
974 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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2k views

Installing Nest 3rd generation thermostat from Old Trane Weathertron Thermostat (Mercury one)

Nest is not detecting Power (Rh) Showing error that power is not connected. Please help. Installing Nest 3rd generation thermostat from Old Trane Weathertron Thermostat (Mercury one) New stat wiring:...
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3k views

Nest thermostat - combi boiler and UFH set up question

We recently had some work done, a new open plan room, a new boiler and underfloor heating (UFH) put in. We had some confusion, a lot of which comes from not having a basic understanding of how the ...
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1answer
227 views

Replacing old thermostat with 2 white wires for zone boiler heat

I am replacing our basement thermostat that had a white and orange wire together and a white and blue wire together. That is all there is. I ham trying to put in a heat only non programmable honeywell ...
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1answer
62 views

Furnace and Thermostat Issue

One day my parent's furnace and thermostat stopped working. The thermostat is a smart thermostat that depends on 24volts to the R and C wire. We measured voltage between the R and C wire and was ...
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1answer
95 views

Direct Wiring (bypass thermostat) of heatpump cooling

Last September my CT80 radiothermostat would not signal cooling despite the measured temperature exceeding the temperature setpoint. It would be nice if a relative could manually switch the cooling ...
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1answer
1k views

Why my baseboard heater won’t turn with new thermostat?

I have a pair of electromod basement heater. The label on each of them show them show 750/1000W. Power supply to this is 240V I am trying to replace the old manual thermostat with a progrmabale one. ...
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1answer
36 views

Where does my C wire go in this splice connection?

I'm looking to install the Ecobee3 Lite thermostat. My current thermostat has a blue C wire running to it, so my understanding is the PEK doesn't help because that is used if you have no C wire. On ...
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1answer
112 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
179 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
379 views

Installing a Hive Thermostat

I purchased a HIVE thermostat and want some assurance before I go about installing this. First of all i was wondering where to put the receiver as I thought it would just replace one of the ...
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1answer
500 views

Is my Nest thermostat wired correctly?

I've been having issues like the heat pump not heating. Now that it's hot outside, my A/C isn't working. Can someone tell me if my Nest thermostat is even wired correctly? If it helps any, here is ...
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1answer
526 views

New Thermostat installed but compressor comes on immediately

I have a new Insteon Thermostat that I'm using to replace my prior Honeywell t-stat. This is installed to a relatively new HVAC system (both AC and Heat) that DOES have a "c" wire. I've attached the ...
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3answers
952 views

Boiler heating extra zones

Background: This is a new house, with a boiler system I'm not familiar with. Instead of zone valves, each zone has its own pump (4 zones). There is a fifth pump on the other side of the boiler. Not ...
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1answer
192 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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1answer
52 views

Another “How do I add ”c" wire to boiler for Nest

I have tried searching this forum and others, but I could not find anyone with a situation like mine. I thought it better to ask here, rather than damage something. I have a Lennox wall mounted ...
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2answers
76 views

Thermostat White-Rodgers 1F82-261 switches to stage 2 heat for no apparent reason

I am running a central heat system that uses a heat pump as stage 1 and a gas furnace as stage 2. The thermostat used is the White-Rodgers 1F82-261 which supports 2 stages of heat. When using regular ...
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1answer
61 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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1answer
37 views

Is the PY4G HVAC unit compatible with Nest Thermostat?

I recently bought a Nest Thermostat and I've had nothing but trouble with it. The main symptom is the fan and the AC compressor won't run at the same time. Power only comes through the green wire, not ...
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4answers
6k views

How to wire a relay for an evaporative cooler to a thermostat?

I have an evaporative cooler with 120VAC control that I want to switch on and off using a relay that is activated when the cool call comes from my thermostat. I plan on just using 1 relay to activate ...
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7answers
105k views

Should I use 12/2 or 12/3 to wire a 220V electric baseboard heater and thermostat?

When I bought my baseboard heaters, thermostats and 220V breakers I was advised to get 12/3 wire. When I attempted to install the heaters I found that the thermostats, heaters, and even breakers have ...
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2answers
320 views

How to hardwire combined HVAC system for cooling?

I had to borrow the Nest thermostat from one of my units for another one where it was more needed, while a replacement is on the way. The unit from which I borrowed is combined HVAC (heat+cool) with ...
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1answer
53 views

Plz help me, connect a common wire for smart thermostat in furnace

I bought a 3rd generation Nest. It doesn’t turn on after I hooked it up. I did research saying I need a common wire as power supply. I have closely look all the wires in my system and drew a diagram....
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1answer
64 views

Weathertron Xl1200 to Nest Thermostat

We have a Trane Weathertron Xl1200 heating pump with the thermostat pictured below and are trying to replace it with our new Nest thermostat. Our old system has a variable speed air handler and we ...
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2answers
69 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
130 views

Central Heat Won't Turn On When I Raise the Temperature on Nest Thermostat

I'm sure my heater is working. It's 47 degrees outside, and I'm only a little cool inside. My Nest thermostat is set to 67 degrees. The screen on my app (which agrees with the thermostat) is shown ...
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1answer
58 views

Why does my thermostat show code 'PF' after running the fan or A/C?

After running either just the central HVAC fan, or the central HVAC AC for just a few minutes, the Bryant thermostat (Model TSTATBBPB101, C Wire attached) screen momentarily shows "PF", and then goes ...
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1answer
202 views

Ecobee Smart Thermostat- Using Room Sensor as primary control

This is ultimately a fairly simple question about the Ecobee3 thermostat and the wireless room sensor functionality, but I'll explain my situation first. Twin home, 2 stories + finished below grade ...
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1answer
124 views

Nest thermostat installation to furnace and heat pump

We have T874G1196 thermostat by york (can only find honeywell documentation) MB7BM-1200K-B air handler H8HK015H-21 electric heater Thermopump (heating and cooling) We want to connect it to a nest ...
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1answer
30 views

How can I control my furnace fan from a secondary thermostat?

I have a WaterFurnace geothermal system with upper and lower level zones. I recently added an outdoor wood burner and my issue is that I want to use a secondary stat to run the furnace fan during the ...
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0answers
28 views

Condo fan coil thermostat fan never turns off, cooling is humid

My thermostat in my condo is a honeywell thermostat and it the only options it has are System and Fan. Fan is set to auto (other option is Lo Med Hi) and the System is set to Cool (or Auto or Off). ...
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1answer
651 views

Can't get 3rd Gen Nest to power fan on Trane XR95 furnace

I have a Trane XR95 furnace and I replaced my original Honeywell Pro 4000 thermostat with a 3rd gen. Nest. I noticed, however, after installing the Nest that I can't get the fan to run on its own ...
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2answers
250 views

How should my third-generation Nest thermostat be connected?

I have an old Honeywell Q674 thermostat with mercury in the house we just moved into. I'm attempting to upgrade to the nest 3rd generation thermostat, however the wiring labels are VERY different. ...
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2answers
3k views

Why is my indoor A/C Blower randomly turning on and off only with Nest?

I recently purchased a Nest Thermostat (3rd Generation). My old thermostat was working perfectly. I wired Nest the Same exact wiring as the old thermostat which is : Y1 W1 G RH RC. With Nest, the ...
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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 ...
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16 views

Ecobee installation with two Rh wires, occupied G wire and HRV

I just moved to North America from Europe (hence why furnaces, HRV systems etc are totally alien to me) and I'm having trouble understanding how to wire up an ecobee3 lite to replace my Honeywell ...