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

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4k views

Why is my Nest thermostat not working with A/C?

I installed Nest thermostat a few weeks ago, replacing an old Lux programmable thermostat (there was nothing wrong with it). I connected 4 wires (R,W,Y and G) to the Nest. But as soon as I'd ...
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1answer
302 views

Wifi Thermostat wiring

Replacing 2 Hunter thermostats with a Honeywell RTH9580 Wifi. Neither unit has a C wire - I'm comfortable with the upstairs high efficiency unit, but the downstairs older unit has thrown me for a ...
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1answer
143 views

How can I consolidate different heating/cooling systems into a single system?

I have 3 different types of heating/cooling systems that I inherited. Hot water heat. This heats the whole house/garage via 3 zones. Zone 1: Kitchen/Livingroom Zone 2: Bedrooms/Bath Zone 3: Garage ...
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1answer
1k views

How to connect Nest in Europe

I found a question regarding the Nest thermostat here. But that is only a question "Will it work?". Thanks to that I know it WILL, the problem is...HOW. I know the wire naming conventions are ...
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1answer
62 views

Is it possible to use add-a-wire with my current configuration to add a C-Wire?

I only have four wires: Red, Blue, Yellow, and Green. My old thermostat jumps the R to RC and leaves C empty. I have a new thermostat that wants 5 wires, but I don't have C. I am not sure what the ...
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1answer
359 views

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

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
103 views

Can I replace this Airwell thermostat?

I am in market to replace my simple A/C control unit with one that integrates with home my z-wave based home automation system. However, before I make the splash and buy a compatible thermostat, I ...
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1answer
234 views

No electricity going to thermostat

Our old thermostat is working but I want to change to a new one (nest thermostat). I have two exact HVAC unit at home. I change one it works but when I change the second one it doesn't work because ...
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0answers
186 views

Are w1 and w2 both energized during a second stage heat call from the thermostat?

Short version: does two-stage thermostat always close W1 circuit when it closes W2 circuit, or they might be closed independently? Long version: I have two-stage furnace, currently connected to older ...
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0answers
20 views

Using a second thermostat to balance temperatures thru fan-only control

Like many others, temperatures between the two levels of my house are uneven. This is particularly noticeable as spring arrives and the upper floor (above ground) enjoys solar heating (so the heater ...
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0answers
56 views

Why won't a NEST that shares control of a furnace with a conventional thermostat turn on the heat?

I have three floors in my home. The bottom floor has its own gas furnace and the 2nd and 3rd floors share another gas furnace. Everything was working great until I added a NEST to the first and ...
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0answers
71 views

Why doesn't my A/C get power when using the alternate C-wire thermostat hook-up method?

I changed my old Honeywell thermostat for a new Honeywell WiFi thermostat. I installed it just as the directions stated. I used the alternate C-wire method as the old unit did not have one. ...
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0answers
124 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 wenter image description ...
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0answers
38 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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0answers
46 views

Why is my heat not shutting off at the set temperature?

When I turn the heat on on my central heat and air unit, the heat came on then continued to run getting really hot. It would not shut off unless I turned from auto to on then back. Sometimes I had to ...
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0answers
19 views

honeywell l8124a114 adding c wire thermostat

Only have two wires. Red and white. Relay at boiler has two existing wires hooked to indicators T and T. Which connection would I use in this system to add the c or constant. Following are locations ...
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0answers
221 views

What temperature should I set on the high limit thermostat of my water boiler?

I have a fairly old (like 1950's) water boiler heating system in my house. There is a Honeywell LA409A Aquastat high-limit thermostat attached to the system. As far as I can tell, the range of ...
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0answers
266 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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0answers
46 views

How do I troubleshoot a gas water heater whose dial doesn't remain set and which outputs luke warm water?

In case it's relevant: Several days ago the pilot light went out. I attributed this to having to use the shop-vac in the area and possibly blowing it out. After lighting it, it went out again after a ...
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0answers
172 views

Why isn't water running through our radiators?

We had a plumber in today to bleed our rads. He also changed the batteries on the thermostat and fiddled around with the boiler. Since he left the temperature has dropped dramatically and he's refused ...