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

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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
254 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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2answers
526 views

Trying to figure out 'C' wire

I'm looking to upgrade my programmable thermostat to a wifi thermostat. I purchased a basic Honeywell wifi thermostat but upon installation could not find a 'C' wire. I started to investigate more ...
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1answer
597 views

How to add “C” wire using a/c fan wire?

Honeywell has a video that shows how to use the fan wire ("G") of the cooling system as the "C" wire for the thermostat. It is in the video - "Honeywell DIY wifi...substitute g-wire for c-wire" on ...
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1answer
100 views

Possible to check NEST system compatibility by looking at current thermostat model?

I'd like to replace my Honeywell CT87A thermostat with a Nest thermostat. I see that Nest has a page to check system compatibility. Is it possible to identify if my system is compatible without taking ...
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31 views

Wall mounted dial thermostat

I recently bought a wall thermostat I broke the plastic front on the box to remove The thermostat as I tried to pull it out of the box the dial came off in my hand and I do not know where it ...
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1answer
878 views

Where is my common wire on the unit?

I have 2 systems in my house, my heat is gas hot water radiator heating and A/C is a separate newer system. I'm trying to figure out if I can run a C wire off air handler from the A/C system to run ...
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2answers
73 views

Is it possible to create a better temperature controlling system?

I have a two story 2.5k sq ft house with a varying degree of temperature throughout the house. The main problem is that the air coming out of vents are very weak if almost nil. Only the living room ...
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2k views

Where to connect a c-wire on a furnace with existing two wire mercury thermostat

My existing thermostat is an old mercury two wire device, heat only. Looking to upgrade to a better model, but I need to run a c-wire. I don't know where to connect the wire at at the furnace, any ...
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1answer
154 views

Should my A/C compressor come on when I turn only the fan on?

I have a bog standard HVAC system with a Nest thermostat. When I tell the theromostat to turn the fan on for 15 minutes the A/C compressor also kicks on. Is this normal?
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51 views

choosing a programmable thermostat: wiring and power

I want to replace my non-programmable RobertShaw 9500 thermostat with a programmable thermostat. The current wiring uses these terminals: RH, W, Y, G. With that set of wires, can I get a ...
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837 views

Which terminal should be used for a “C” wire when none are labeled “C”? Older electric furnace/heat pump

I have an all electric air handler/furnace connected to a separate AC unit and it is also a heat pump. I've purchased the latest and greatest Honeywell WiFi "Smart" Thermostat and it needs a C wire. ...
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1answer
351 views

How to connect a DIY thermostat to the HVAC System

I am building a DIY thermostat similar to this blog. I want to connect it to the HVAC system of my home. How do I do that? I found this post which is very informative but doesn't completely answer my ...
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2answers
3k views

Can I install a Honeywell WIFI Thermostat?

I have done quite a bit of research and have not been able to find an answer I am looking for. I currently have a manual digital thermostat that is not programmable made by Braeburn. My system is a ...
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1answer
315 views

Is my thermostat transformer voltage too low?

I measured the voltage at the thermostat Rc to G and Rc to Y terminals, and they read 16.2V and 16.34V respectively. Shouldn't I be measuring 24V+/-? I purchased a Nest thermostat and it will not ...
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1answer
557 views

Please help establishing a C wire for new tstat

I bought a new WiFi tstat as a replacement. The tstat controls my second floor hot water baseboard heat and my central air conditioning. I've located all the wires....the ones coming up from the ...
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2answers
240 views

Replacing old thermostat with new wi-fi Honeywell

I'm trying to replace my old mercury thermostat with Honeywell Rth8580wf. The cable has 8 wires, only 4 were being used. The wire colors and letters on the thermostat do not match up, so I'm left with ...
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1answer
2k views

Need help running and connecting a 'C' wire to my new thermostat [duplicate]

I have a Laars gas boiler that has 3 heating zones; basement, 1st floor, and 2nd floor. I want to replace the old mercury honeywell tstats on the 1st and 2nd floor with newer honeywell RTH9580 wifi ...
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1answer
50 views

What should I do with an old thermostat? [closed]

I recently had a security system installed which also included a replacement thermostat. Should I just throw this old one in the trash?
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1answer
3k views

How do I add a C/ Common wire to my “Specific” HVAC system? [duplicate]

I just bought a new WiFi thermostat that requires me to add a C-Wire at the furnace. I have read the questions related to my issue but would like a suggestion on my particular (incredibly OLD) ...
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1answer
382 views

Thermostat C-wire replacement using a wall socket?

I have a Filtrete 3M WiFi thermostat. As expected, it takes a C wire, which my apartment doesn't have and the apartment maintenance folks wont' let met wire either. However, there's a wall socket ...
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3answers
2k 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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1answer
2k views

How do I turn off the power to my programable thermostat?

I am installing a new programable thermostat. In trying to cut power to the old one I have tried a couple of things but not sure I have done enough to cut all power. One, I shut off the furnace ...
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1answer
301 views

How can I replace a 4-wire manual thermostat with a programmable thermostat?

I"m replacing a 4-wire manual baseboard thermostat with a programmable SBFT2W thermostat. After connecting the wires, there are two lead wires from the old stat that are still unconnected. They are ...
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0answers
43 views

I changed my thermostat, not my heat does not work… help!

I know I made a mistake, but here's the storey. When I was hooking up the new thermostat I did it with live wires, and I used metal pliers (metal touching metal). The wires may have also touched ...
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0answers
27 views

Thermostat has broke - need help with the wiringl

Im changing from wn old White-Rodgers mercury thermostat to a Honeywell digital thermst. And The directions for the digital one says I am to label the wires from the old one-then hook the wires into ...
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1answer
10 views

RUUD Furnace blowing air but not heat

I have a RUUD furnace that stopped blowing hot air last night. I was thinking that it was the high limit switch gone bad BUT the coil ignites and lights but then goes out again after a minute, so ...
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2answers
22 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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0answers
48 views

How do I get a wifi thermostat for a line-voltage electric heater?

I have a 120v radiant heater. Currently it uses a thermostat PSG 120HS/55NL (3 wires Line, Load, Neutral). I am looking for wifi thermostat that I could control with my phone. I see several ...
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1answer
64 views

Diode in a link wire for Thermostat?

What I have is a back boiler that runs my central heating via a pump. The domestic hot water is gravity fed. At present I have to turn the domestic hot water on via a timer switch this then gives me ...
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1answer
34 views

Why might a central heating programmer no longer override a room thermostat?

My central heating and hot water is governed by a Danfoss FP715 Si. Using this I can set the time each day when the central heating and the hot water come on and off. When the central heating is on it ...
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1answer
161 views

Add a c-wire to 25+ year old Rheem furnace

I've looked at just about every post on adding a C-wire to power a WiFi thermostat but remain uncertain on how to proceed. The current installation on a Rheem RGAC-080A is two wire as here: XFMR - ...
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76 views

My furnace has a C - common wire but air conditioner uses it - how to hook up smart thermostat?

I bought an ecobee3 smart thermostat which requires the C wire. At my furnace there is no circuit board but there was a diagram and I was able to locate the C - common wire, but it seems to be used ...
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0answers
16 views

Can I use the unused brown wiring for my old thermostat for Nest Thermostat’s advantage? [duplicate]

Here are the images I figured out all the other connections as W/W1, Y/Y2, G, R & C but the brown wire is not connected to anything. What could that be for? Edit: From this answer I figured it ...
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0answers
81 views

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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1answer
92 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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0answers
6 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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0answers
189 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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39 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
112 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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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
52 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
42 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
30 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
132 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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0answers
39 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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255 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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0answers
124 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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0answers
205 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?
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42 views

Thermostat needs to be set very high to work

Our home thermostat is behaving strangely. Let say it shows that the current room temperature is 60F. If we set it to 63F it will start the Fan (ventilation) but will not actually start the heating so ...