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

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Need a furnace/air conditioner C wire, but can't make permanent modifications

I live in a rented apartment, so I can't do any permanent modifications to fix the problem. I have a basic WiFi thermostat that requires a C wire, and the heater/air conditioner is just old enough to ...
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3answers
180 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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1answer
42 views

Thermostat/electrical

I have a Honeywell RTH2510 series thermostat that I want to install in a condo with baseboard heating. I took off the very old thermostat that was previously installed and there are only two very ...
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2answers
62 views

Rented Property: Install Nest

I have a Worcester boiler (Greenstar HE?), with a TR2 thermostat. I was looking at replacing the thermostat with a Nest (or equivalent). To complicate matters, I'm in a rented property, so I cannot ...
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2answers
72 views

Electric baseboard wiring

I have a 240v 1500w 6.5a electric baseboard heater with a wall mounted thermostat. What I found out is that the the thermostat and all the outlets in the room are on the same 20a breaker with this ...
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1answer
195 views

Can I shorten my in floor heating cable?

Just wiring up an in floor heating thermostat. I have two separate two wires going into my flooring as well as another coming from the panel. I am wondering about the two wires going down to the ...
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1answer
38 views

0v at DC thermostat terminal in furnace

I have an old (mid 80s) Rheem gas furnace I hope will last me through at least one more California winter. It's been known to go down into the upper fifties, so it has its work cut out for it. In any ...
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0answers
7 views

Can I use any C terminal on a furnace to supply power to a thermostat? [duplicate]

I have a dual heat system with a gas and electric plenum. trying to install a wifi thermostat and found that the C wire on the furnace is connected but once it goes up and through the electric plenum ...
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217 views

No C wire terminal on my electric plenum but there is on my furnace. How do I solve?

I had a brand new furnace installed recently but also now picked up a wifi thermostat. The problem I now encountered while installing the thermostat is that my system also has an electric plenum as ...
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1answer
161 views

Can I share “C” wire on two thermostats?

I am wiring a second thermostat right next to the original one. The new needs a C wire. Can I share it from the old one? Old: 8 wires, used to run heat pump (w/ heating and AC) and backup oil. Now ...
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44 views

Home still heating after unit is off

My wife and I just purchased our first house and we're having an issue with the house getting too warm. We usually set the thermostat to 65 while we're sleeping when the unit reaches that temp it does ...
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1answer
273 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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2answers
1k 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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1answer
82 views

electrical range - oven temperature not set

I have a pretty old electrical range GeneralElectric RCBS536DN2WW. The problem is that I can't use the oven: whenever I set the temperature with a temperature knob, it raises up rapidly and everything ...
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1answer
32 views

Find the model for an unknown (non-Häger) wall thermostat?

I recently bought a house, after years in a flat. Many things are novel to me, especially the heating system. The digital thermostat is of an unknown brand, the former owner could not tell me (I ...
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1answer
287 views

Can I use a ground instead of a dedicated C wire for a thermostat

My new wi-fi thermostat requires a common wire coming from the 24 volt transformer. Rather than running an additional wire can I ground the common side of the transformer to the building steel ( this ...
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1answer
50 views

How does my Boiler work with my Baseboard and thermostat

In the apartment I am at I am just wondering how the boiler system works between all the units. Apparently its one water pipe going the whole perimeter of the floor but each apartment has it's own ...
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0answers
22 views

Zoned heating problem

I have a 2 zoned Trane forced hot air gas heater with a Honeywell control board,2 thermostats. One in the basement one upstairs. It's a rancher. When heat or air is called for upstairs it goes on ...
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1answer
79 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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0answers
48 views

How can I check if my boiler room thermostat is working?

I have an old Honeywell basic thermostat and I am not sure if it's working properly or not. I doubt it because the boiler stops burning after some time even when I set 30 °C on the thermostat and ...
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0answers
31 views

What is this heating thermostatic head connection called?

I want to purchase and install thermostatic head for heating radiator valve in my room but can't identify connection type. The radiator itself and valve don't have manufacturer name on it. What is ...
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2answers
308 views

Thermostat wiring splice

I need to relocate a thermostat and have the additional wire needed but I am not sure of the ideal way to "join" the cable sections. Will using wire nuts and zip tie be good enough?
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27 views

How to connect 4 fan coils with one wall control thermostat?

I have 4 fan coils (Sabiana sk-22)and I want to connect them with one wall control thermostat. How can I do?
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2answers
109 views

Is the Thermostat Wiring Correct

When I moved in to the house the first thing I changed was the old mercury style T-stat to a digital one, I went wire for wire, and it has works (knocks on wood) so far. Now that I have been reading ...
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1answer
474 views

Where do attach C wire on my boiler?

I need to add a C wire to use my wifi thermostat. I have a 2 wire thermostat now. There is a third wire in the wall which runs to the basement where it is cut off. I can easily extend it to the ...
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1answer
247 views

Furnace reaches temp, shuts off but wont come back on

I have an American Standard furnace (natural gas)with a manufacture date of 2004. The thing won't come on unless I power it off (have a switch right beside it that serves this purpose), let the fan ...
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1answer
104 views

central A/C Turns back on 30 seconds after shutting off

First of all, the a/c system is probably 30 yrs old. The outside unit stays running when the inside unit shuts off. After about 30 seconds, the inside unit turns back on again, and will sometimes only ...
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1answer
78 views

When running AC, Heat turns on once thermostat reaches desired temperature

I just recently installed a new wifi thermostat for my system. I went from a Trane to a Honeywell. I followed the instructions and put the wires in the right terminals (i believe) Everything is ...
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1answer
308 views

Help installing new thermostat

disclaimer, this is my first attempt at doing any type of electrical work, so apologies in advance for any wrong terminology :) I attempted to install a new Honeywell programmable thermostat. When I ...
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2answers
195 views

trouble shoot air conditioning thermostat

my compressor outside is not kicking in. Here's the sequence of events: I came home and the thermostat - a Honeywell LCD - was no more numbers and the battery indicator was flashing. replaced the ...
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2answers
1k views

How can I wire my WIFI thermostat to control my millivolt fireplace?

I have a gas fireplace that has an millivolt on/off switch on my wall (and a remote that includes flame on/off, a countdown timer and a thermostatic flame control). I want to be able to program ...
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1answer
86 views

switching out a heat/cool only thermostat to one with “auto” feature

I have a Honeywell deluxe programmable thermostat with a sub-base... Sub-base: 32207415-011/0008 Model: T8602D2000 The terminals that are used currently are: R W Y G (RC and O are not used) My ...
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1answer
38 views

Thermostat broken or central air system?

Thermostat works sometimes, other times I have to shake the switch to get the air conditioner working. Is this a problem with the thermostat or the central air system? Thermostat is about 15 years ...
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1answer
44 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
41 views

Should I install a doorway fan or dehumidifier?

I have central air in a rancher (one floor), and the living room is on one end of the house. That room is on a slab, and has always been noticeably hotter in the summer and colder in the winter than ...
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1answer
407 views

Honeywell RTH7600 does not responsd

Just installed new Honeywell RTH7600. All wires are correct and the unit displays fine. The issue is that heater and AC do not turn on at all. I even put the fan to ON instead of AUTO and that does ...
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1answer
131 views

AC continues to run for several minutes after shutting off

When I turn off the AC it continues to blow cold air for several minutes. I realize this may be an energy savings feature, but I'd like to know if it is possible to disable it. In other words, what ...
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2answers
1k views

Can I use a WiFi thermostat without a C wire?

I have a very old Honeywell programmable thermostat. I am going to replace it with a White-Rodgers UP500W Emerson Sensi WiFi Thermostat. I just want to know if the WiFi unit will work without a C ...
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0answers
43 views

Residential HVAC: one main thermostat, what do the other thermostats in the rooms do?

Are the other thermostats only meant for non-force air heat only? Does it mean only one thermostat in the house needs to have both heating and cooling, and auto or fan-only switches? It sure make ...
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0answers
375 views

AC Compressor outside is not running with new thermostat

my old thermostat stopped working, so I purchased a new one to replace that. The old one was powered by two AA batteries. A green wire connected to G, a white wire connected to W, a blue wire ...
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1answer
33 views

Issue with Thermostat

I bought and installed a Trueway thermostat before 2 years. It was working well for the past years. But then a twist! the thermostat started to go nuts, the tempeature would race over 60 degree, even ...
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1answer
229 views

How to override an attic thermostat with a wall switch?

I want to install a fan in my attic. I want the fan to be controlled by a thermostat in the attic, but I want the ability to bypass or override the fan from within my house. Ideally I would like to ...
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0answers
167 views

Changing Trane Baystat240a to another thermostat

I want to change my current thermostat to a programmable electric one (no batteries). Could someone verify if it does have a common wire and if all wiring could fit modern thermostats? Looking at the ...
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2answers
713 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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1answer
272 views

Where is my Common Wire? [duplicate]

I purchased a wifi thermostat and cannot located the common wire. My unit is old and is a Coleman 70 with no terminals inside labeling the wires. As you can see in the second image, there is a ...
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1answer
288 views

How can I tell if I have a C wire?

Below is a photo of my current thermostat's wiring. I have a few questions: Why is the RC and RH are bridged with a black wire? I have an unused blue wire. Is there a way to find its function? Could ...
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1answer
2k views

Can I connect two wires to a single screw terminal in my HVAC system?

I am installing a new honeywell WiFi thermostat but the old battery operated thermostat had batteries and no "C" wire. I look at both the thermostat and the air handler and found an extra un-used blue ...
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1answer
115 views

How to Change Chinese HVAC Thermostat

I am looking to put Nest thermostats in the house, I have now found out my entire house (one in each room, 6 of them) has been wired with HVAC Chinese U12A UNIVERSAL A/C CONTROL SYSTEM urrgh – they ...
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2answers
404 views

Smart Thermostat - No C-Wire - No Controller Board

This one seems to be a little different from previous questions on the subject. Here is the dilemma, I don't see a transformer. I have included a few pics. There are Three wire bundles. For ease ...
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213 views

Why would my AC turn on and off randomly?

My AC unit turns on and off randomly regardless of whether the thermostat is set on or off. I've even tried removing the batteries. Does anyone know why this might happen?