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

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Honeywell home ventilation system with no c wire for thermostat. How can I substitute the g for the c without blowing a fuse?

I'm hoping to get some help with my thermostat problem. We bought our home brand new and it came with a very basic thermostat (non programmable and runs on batteries). I want to upgrade it to a wifi ...
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2answers
255 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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1answer
142 views

How do I connect a C wire to an Utica PEG112CDE steam boiler?

I want to upgrade my old mercury thermostat that I currently have to a newer programmable thermostat. This little DIY project is for my first late 1920's home that I recently purchased. I currently ...
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1answer
575 views

Where do I connect my C wire from my thermostat when there are two transformers?

I have a Laars gas boiler that has 3 heating zones. I want to replace the old mercury honeywell tstat on the 1st floor (heat only) with a newer honeywell RTH9580 wifi model. I've taken pictures of my ...
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1answer
173 views

Can I connect an additional wire to HVAC system where all the terminals are full?

I'm installing a new thermostat (ecobee Smart Si) and it requires "C" wire. I checked before I bought, and saw an unused blue wire behind my current thermostat. However after connecting everything the ...
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1answer
222 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
2k 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
95 views

Where do I connect the C wire in my furnace?

I am upgrading my thermostat to a Nest, and would like to add a common wire. My current furnace controller doesn't have a C terminal, but the current thermostat wire has 2 unused wires (black and ...
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1answer
217 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
92 views

Why did I have to change the wiring to use a smart WiFi thermostat?

I just installed a Emerson Sensi wifi thermostat.It works, and I ran a separate C wire. I had a 24 volt 5 wire Robertshaw programable thermostat that ran my boiler, air handler and AC. It is all ...
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1answer
110 views

How can I replace an old dial thermostat on an oil furnace with Hydrostat 3250 Plus?

I recently bought a home with an oil fired Biasi furnace that has a Hydrostat 3250-Plus attached. It uses an old analog round dial thermostat, and I'd like to replace it with a new digital (wifi) ...
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1answer
27 views

thermostats for high desert climate

We live in Spokane, WA, a high-desert climate. We don't need a programmable thermostat, but we do need one to keep an constant ambient temperature range. This may mean A/C during the day, and heat at ...
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1answer
473 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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1answer
418 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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1answer
266 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
348 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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1answer
401 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
167 views

How do I install a WiFi thermostat with a Well-McLain steam boiler?

I have a Weil-Mclain 150000 BTU steam boiler, and have only 2 wires connected to my thermostat, but would like to add a new Honeywell WiFi thermostat. I have no C wire, no A/C, or any other type of ...
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0answers
263 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
31 views

Keep finding thermostat on heat

On multiple occasions now, I have noticed odd things going on with my HVAC system, only to go to the thermostat and find that it has been set to heat! This happened once in the middle of summer, when ...
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0answers
120 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
97 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
86 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
26 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 ...
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13 views

Zones and setback thermostats

I've got a two-floor house, forced-hot-water and traditional radiators, with a thermostat and zone for each floor. I'm working from home at the moment, so the ground floor is set up to be "office ...
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0answers
86 views

Honeywell WiFi Smart Thermostat Wiring

The Honeywell WiFi Smart thermostat was operating fine when on AC until the heat went on this fall. Now, each time the fan goes on, the thermostat loses the connection, turns blank, then reboots ...
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0answers
21 views

Updating thermostats to single system

I have a three floors in my house, each controlled by it's own thermostat (separate air handlers and mechanical valves on furnace). Baseboard heat. The three thermostats are controlled separately, ...
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0answers
32 views

How can I install a Honeywell Linevolt Pro 8000 in a multiple thermostat situation?

My roommate who just moved out installed a Honeywell Linevolt Pro 8000 in his room several months ago (replacing an M602 with no brand name that I can find) and it seems to have worked fine - it had a ...
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0answers
501 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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0answers
18 views

Why does adding 2nd Wifi thermostat not work in 3 zone home?

Our home has 3 zones for forced air heating by oil and central AC. I replaced a Robert Shaw thermostat with a Honeywell Wifi unit and it worked fine. I then replaced another Robert Shaw thermostat ...
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207 views

Furnace not working properly with digital thermostat

I have been attempting to use several different types of digital thermostats to replace my old mercury thermostat, however none of them are able to control the furnace properly. All of them are able ...
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78 views

Thermostat replacement

My old thermostat is a carrier t-stat and has a jumper wire between o/w2* and L I am upgrading to a honeywell wifi t-stat, should I install the same jumper wire on the new thermostat? I have an ...
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51 views

Connect Taco Radiator system to a new Honeywell wireless thermostat

I have a Taco model 572 valve connected to an existing wired Honeywell TH8110 thermostat for my oil fueled radiator system. I'm getting a new Honeywell TH6320 wireless thermostat for a new A/C ...
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0answers
208 views

Master-Slave type Thermostat?

I have 4 thermostats located in four different zones and a separate AC thermostat. I want to get some programmable thermostats for each location. I could buy 4 individual programmable thermostats ...
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0answers
101 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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45 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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312 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
215 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 ...