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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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1answer
38 views

Propane wall furnace not firing

I have a propane wall furnance that is'nt firing, the thermostat is not appearing to trigger the unit. The pilot is fine and the thermostat is a simple unpowered one with mercury that appears to be in ...
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1answer
440 views

How to remove the wall plate behind Honeywell thermostat

I'm trying to install a smart thermostat. I have a Honeywell programmable thermostat now. However, I found that there's a wall plate in back of the back plate, and it's secured to the wall (not by ...
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1answer
52 views

C-Wire identification

I am interested in replacing an older thermostat with a modern networked 'smart' thermostat \ humidity monitor. That being said, does the photographed thermostat have a C-wire? The thermostat ...
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0answers
205 views

Adding C-Wire for Nest to Triple Aquastat Relay L8148J

Need some extra eyes and advice on how to add a common wire to our current boiler setup. We have a Triple Aquastat L8148E that has 2 wire that connect to our thermostat. Like many before me, I'm ...
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9 views

Jumping AC fan to separate Gas Boiler Heat

I have 4 zone boiler/baseboard heat and a new Trane XR 5ton central A/C system. I also have a woodstove that is mainly used for heating except at night when the upstairs are closed. I just got the AC ...
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1answer
2k views

Where to add C wire on this air handler?

Thanks for helping me here. I am adding a new wifi thermostat to my system but need to add a C wire directly to the air handler (system is a First Co air handler with hot water boiler for heat and ...
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1answer
97 views

Why is my thermostat turning the heat on too soon?

I have recently come across an issue with my thermostat and when and how my heat comes on. My thermostat seems to be an old round Honeywell. I set my temp at 65 typically. As of last night my ...
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147 views

Using T-Terminal for C-Terminal on Lennox Furnace — Thermostat will not power

Furnace: Lennox Pulse Thermostat: Honeywell RTH6500WF I have the similar setup as the person in the below link Can I use the T terminal in my furnace as the C for a Wifi Thermostat? When I ...
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17 views

how to communicate thermostat to turn on wood heat system when during heat pump defrost cycle

I have physically disconnected the strip heaters in my air handler but the fan still runs which I do not want. I have a wood boiler I want to run in place of the aux heat Can I disconnect the white ...
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20 views

Not sure what colors go to my new thermostat

Not sure what colors go where from my old one to my new one the old is on top and new is on bottom
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2answers
25k views

Why “W” (heat contactor) and “E” Aux Heat connected in Thermostat

I'm trying to update my thermostat to one that has a scheduling feature. My plan is to just copy how it was hooked up in an old 129N Thermostat from Armstrong however, I can't figure out why the "W" ...
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14 views

Lost on how to set the comfort range

I am hoping someone can help me. I have read through the questions and answers on here but I am still lost. I have the same GeneralAire M3 thermostat and it does not indicate to me what the percentage ...
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1answer
53 views

Can't find HVAC C terminal

Could any of these be the c terminal on my hvac unit? There's already a c wire there, just can't figure out where to connect it.
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2answers
13k views

Can I use the T terminal in my furnace as the C for a Wifi Thermostat?

I've read many posts on this, and believe I know what to do, but want to make sure. My furnace (a Lennox G14 Series) does not have a C terminal which needs to be connected to the C terminal in my new ...
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3answers
51k views

Hvac Fan only blows in 'fan on' mode while heating

Our HVAC Fan only blows in 'fan on' mode while heating. In other words the fan will not blow in heat mode if switched to "fan auto". Both fan on and fan auto modes work when cooling. See image below, ...
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373 views

Nest 3rd Gen 24VAC two transformer issue

Hopefully this will finally solve the issue with my Nest. I bought a Nest 3rd Gen Learning Thermostat and followed the instructions to the tee. I have a two transformer system (Forced Air A/C and ...
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0answers
22 views

Furnace, heating when thermostat is at much lower

I have an oil furnace that heats the house with water pipes, and heats the hot water used personally. There are two thermostats used, one for the house and second for the back porch. The issue is ...
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35 views

Fan Blows Constantly Even With C Wire

Nest stated that my furnace only set up (we have an evap cooler) would work with their Nest E product. I self installed only two wires, R and W. The heating works; however, the fan always blows ...
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1answer
158 views

Zone Controller T-Stat Wiring w/ 24V transformer, isolation relays for 2 zones

I have a new Navien SmartZone+ 6-Zone Control for my boiler-based heating system. It is great, except it provides no power on C. I realize the internet has researched the heck out of adding a C ...
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1answer
789 views

UK Nest Installation - Underfloor heating including floor temperature sensor/cutoff

I would like to use Google Nest with my underfloor heating system which is under a wooden floor. Other thermostats allow the user of a floor sensor which monitors the surface temperature of the floor ...
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0answers
52 views

Heating System Premature CutOff / DIY Options?

I've collected all of the facts about my system and the problem we are seeing. We have two external air pump units outside the house and a Rheem furnace (GH36S, 36000 BTU) that appears to be working. ...
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0answers
40 views

How to identify a c wire?

I have 3 wires coming out from the wall at my new house (red, white, blue). It is a water boiler heat only system. The tstat was already removed unfortunately. I thought the blue wire was the C wire, ...
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17 views

Mercury thermostat behaving strangely

I reinstalled an old mercury thermostat. Heat and air both work, but they won't cut off until I move the thermostat switch to Off. In other words, when the switch is on Heat, the furnace and blower ...
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0answers
87 views

Thermostat has two wires going into C terminal

Trying to help my dad install his new Nest thermostat - for some reason his thermostat has two wires going into the C terminal. I've searched and cannot find any other question about a setup like ...
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1answer
46 views

How long you can keep gas furnance heater bypassing thermostat

Thermostat is broken but needed to heat the house. I decided to jump R and W wires to get some heat this cold night. The question is for how long I can run the heater (gas)? Is it Ok to leave it on ...
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2answers
127 views

Electric baseboard heater thermostat.

My the upstairs of my house is filled with electric baseboard heaters that use these thermostats that are mounted right on each heater. My house is a bungalow and the upstairs gets no heat or AC. ...
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0answers
43 views

Lennox G12D2E-55C-6 with a Johnson Control G779LHA-1 ignition control and Mercury Thermostat

I am looking to replace the mercury thermostat with a Lux Kono thermostat simply to have the ability to run the fan only and circulate the air. I believe this thermostat does that periodically. I'm in ...
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0answers
32 views

AC Common wire disappears

On my furnace there is a wire that is labeled C/Common. But at my thermostat there is no common wire. Wires on furnace control panel: W - White Y - Yellow G - Green C - Common Wires at my thermostat: ...
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2answers
3k views

How can I connect a WIFI thermostat to a Honeywell R845A switching relay?

I'm trying to install a wifi thermostat and it won't power up. The old thermo was battery operated 2 wire but there were spare wires. At the R845A relay, red and white whites connect to terminals 5 ...
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1answer
197 views

Can't get fan working on thermostat

I recently purchased a new thermostat. My old thermostat worked for heat (no AC either) but the fan wouldn't go on when I turned to "On" (in hopes to move some cool air from the basement up during the ...
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0answers
25 views

thermostat issues with honeywell

I've gone thru 3 thermostats in the last 6 months, and the temperature on them goes wacky. I've tried everything except call someone. is there a trick or solution. this is the third honeywell ...
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4answers
5k views

Can a wifi thermostat to control milivolt operated fireplace?

Have a propane gas fireplace, controlled by a hand held remote control thermostat. Wish to install a wall mounted wifi controlled thermostat, heat only. Seems that all available thermostats operate ...
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3answers
12k views

Thermostat is completely blank. How to troubleshoot

I have a thermostat that is completely blank (no display). I'd like to troubleshoot it myself even if I do ultimately hire a pro! We're in sunny southern california, so it's possible it's had no ...
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2answers
6k views

Need help wiring a new double pole line voltage thermostat

[ Just bought my first home and this is my first time posting, so please forgive me if my terminology is incorrect. I currently have bedrooms upstairs each with 1 baseboard heater and thermostat for ...
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0answers
44 views

Can a Nest work in my setup (or am I stuck with Lyric, as they claim)?

Before crucifying me for the subjective question let me clarify that my question is quite specific if you read on. I bought an old home with bad insulation and a 55-year-old furnace 3 months ago. I ...
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1answer
111 views

nest 2nd gen, no common wire/terminal in the fan coil unit

I'm trying to install an older nest in my condo but it immediately complains that there's no common wire attached (error e24). I opened up the fan coil in my condo and there is no specific terminal ...
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0answers
24 views

Need C wire for Nest thermostat with zones. From zone panel to thermostats?

If I have a C wire connected from the furnace to the zone panel (but not to the thermostats), do I only need to run new C wires from the zone panel to the thermostats?
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1answer
89 views

What powers a Nest thermostat? [duplicate]

I have an older thermostat I'd like to replace with the more modern Nest thermostat. The online Nest compatibility checker tells me that I have a compatible device. However, I'm not sure how it could ...
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1answer
67 views

Install Hive Thermostat - C wire power

I am installing a Hive Active thermostat. My previous thermostat was battery operated and did not use a C wire. However, I found a 5th, blue wire, behind the thermostat so I used that as the C wire ...
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2answers
298 views

Nest E Thermostat Power

My thermostat is in the basement, connected to a Honeywell R845A to run a circulating pump for heat. I bought an Nest E for the main house and it works great. I want to replace the thermostat in the ...
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1answer
52 views

Will a Gledhill Boilermate 2000 work with a Honeywell Evohome thermostat?

Our flat uses a communal CHP system, with a Gledhill Boilermate 2000 in our flat (i.e. we don't have direct access to a gas boiler). We're looking to set up a Honeywell Evohome system consisting of a ...
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0answers
36 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
1k views

Honeywell thermostat oozing yellow and programing not working

I installed a Honeywell thermostat last year for our boiler and it worked perfectly. This year we were having issues with it not following the program schedule. The thermostat should be sleeping and ...
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1answer
61 views

Honeywell thermostat issue

I have a Honeywell thermostat with M-F schedule like so... 6:30 am (wake) - 70 6:45 am (leave) - 63 4:00 pm (return) - 70 9:00 pm (sleep) - 63 The Honeywell actually displays wake, leave, return, ...
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1answer
47 views

Will my wiring setup work with the Nest Thermostat?

I would like someone who is smarter then me to let me know if this current wiring setup would work with the Nest Thermostat? Thank you for your help
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1answer
61 views

How do I create a C wire? [duplicate]

My furnace is old and only has 4 wire connections, but I require a C wire. How can I create one based on this diagram? I do have 5 wires running between the furnace and thermostat.
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5answers
4k views

Is there a filter-reminder thermostat that uses run-time instead of total time?

My HVAC filter is in my crawlspace and is a hassle to change. I don't want to change it more than needed. "Change it every month" is bogus advice because in some months (like May) we don't have to run ...
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0answers
45 views

How can I use home automation with hot water heating radiators?

My apartment (in a condo building) is currently using stationary PTACs (using electricity and hot water), which I'm planning to replace with a split-level A/C system (for cooling) and hot water ...
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2answers
220 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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1answer
346 views

nest 3rd generation compatibility with honeywell

My home has a honeywell thermostat (THM5421C)! It has 3 wire: DATA,R and C. Humidifier is Aprilaire 700 Series and Furance is Armstrong A97USMV! furnace side: The wire connection as below: Is it ...