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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3answers
8k views

Do thermostats coordinate with each other in a multi-zone system?

Say I set my thermostat to 72 F. (Yes, I'm in the crazy U.S. and use their strange measurement system). I am under the impression that an HVAC system will wait for the temperature to be off by a ...
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1answer
31 views

Old electric baseboard heater thermostat wiring

I have a question about an old federal pacific baseboard heater thermostat's wiring. I disconnected this thermostat 2 weeks ago, thinking that we were going to remove the heater. Now we've decided to ...
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2answers
34 views

Replace thermostat wiring from my Carrier Weathermaker 8000 to my Nest thermostat

I'd like to replace the wiring from my Carrier Weathermaker 8000 to my thermostat to add a C wire. I assume I need to turn off the Carrier first, but there is no power switch that I can see on the ...
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1answer
46 views

Finding Common Wire on Laars JVT boiler

Replacing mercury thermostat with wifi. I have just a red and white wire connected to current thermostat and boiler. There is a green present, but it isn't hooked to anything on boiler. So I can ...
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1answer
47 views

C Wire in Air Handler

Can someone please help me find where to connect a C wire for my smart thermostat? Here are some pictures with descriptions. It is difficult to get to the 24v connection in the back. My schematic ...
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1answer
44 views

Temperature monitoring for storage hot water system (RP-2 connection)

My HWS has a secondary outlet connection I don't use, and I'd like to use it to install a thermal probe I can monitor. HWS RP ¾ / 20 temp probe? Does anyone know of a practical way to install a ...
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2answers
2k views

Why might a thermostat refuse to switch from Heat mode to Cool mode?

I have this Honeywell RTHL2410C programmable thermostat and typical Florida electric AC system. Starting this Spring, it has started behaving strangely when switching from Heat to Cool mode. The ...
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1answer
15 views

multiple thermostat boiler connection

I have a boiler system with thermostats and valves for three floors. before i changed the boiler what ever thermostat called for heat worked for that floor. Now all thermostats have to be on or ...
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1answer
59 views

My thermostat and heating system was working fine but the batteries read low power

So my Honeywell non WiFi Thermostat was working fine except for the low battery signal in the top right-hand corner. We took the face off of the thermostat of course shutting the Heat and fan off ...
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1answer
336 views

Connect C wire Lennox G16

I bought a new thermostat that needs the c wire. Old thermostat wasnt using the blue c and was stuffed back in the wall. Come to find out the blue c wire is not connected to the furnace. Trying to ...
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2answers
126 views

Misbehaving/inaccurate thermostat?

I have a portable air conditioner/hvac and I'm having issues with it in heating mode. It's actually summer where I live but it was somewhat chilly as a storm passed over so I wanted to test heating on ...
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1answer
592 views

Wiring a C (common) wire to a Triangle Tube Prestige Excellence 110?

Wiring noob here. Can someone give me step-by-step instructions for where and how I should attach a C (common) wire to a Triangle Tube Prestige Excellence 110 boiler for a ecobee3 thermostat? I think ...
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65 views

Problems with my thermostat

My thermostat will turn on the baseboard electric heater but will keep running till you turn it all the way off.
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58 views

Complete power loss in over-the-range microwave

The over-the-range microwave in my kitchen (GE, 1500W) has completely lost power. The power loss was intermittent for a day, but then at some point it never came back. I have checked all fuses that I ...
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2answers
2k 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
188 views

Ecobee3 Setup and furnace only has W G R

My existing thermostat has 4 wires (missing C) so I'm attempting to use the Power Extender Kit (PEK) at the furnace control board. Only problem is, I only have 3 wires that are obviously labelled at ...
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2answers
1k views

Why does hot air from my fan heater stop after 4 to 7 seconds?

Product: Challenge fan heater: model E9907R-N -- 230-240V -- 50 Hz -- 2750-3000W. While off, something fell through the grid. I opened the fan heater to remove it. It now doesn't blow hot air (...
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1answer
28 views

Switching from a Mercury Switch Thermostat to a XT500C Thermostat

I only have a white, red, green and yellow wires, from my old thermostat. I see multiple Red wires... where does a single red wire go... to the R connection...
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1answer
203 views

Adding a C wire to older 3 wire

How do I use the green wire as a C wire as suggested in most installation instructions for the newer wi-fi thermostats? They all reference terminal strips at the furnace, all I have is the 3 wire ...
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1answer
108 views

Ecobee3 lite connected to Lennox Pulse G14Q Heat/Air Condition

I have read a similar wifi thermo connection feed here and they had success hooking the C wire to the T terminal on the furnace. I can get power to run the thermo from the T terminal, but when I do, ...
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2answers
2k views

Nest thermostat gen 2 won’t turn off furnace

I’m struggling to find a solution for my furnace. It’s an older Lennox furnace and runs fine. The problem I’m having is that it keeps burning up my thermostats and once it does it won’t let the ...
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0answers
44 views

Replacing old thermostat and two unidentified wires

I'm replacing an old thermostat from the early 90's with a new wifi thermostat. When removing the old one, it only used R,G,Y,W wires, and the new wifi thermostat requires a C. After fully removing ...
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0answers
32 views

Only getting 15-16 volts from Furnace R and C

I recently purchased a smart thermostat. Because it needed a common wire and I only had a 3 wire setup, I ran a new thermostat wire to my furnace. However, I now get only 15 volts (inconsistently, ...
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1answer
708 views

Thermostat wiring with external transformer

So I am trying to wire a Honeywell lyric thermostat and I tried following videos but got a little stuck. So I have wires R, W ,Y , G coming to my original thermostat. I bought an 24V external ...
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1answer
62 views

Rapid on/off cycling of furnace

My 50-year old wall furnace keeps cycling on and off as it gets near the set temperature. Can I fix this by changing to a new thermostat? It's a 2-conductor cable (no blower).
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1answer
1k 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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1answer
2k views

Where to connect my “c” wire on the boiler side. Weil mclain gas boiler

Im just curious if the “c” terminal on the plug in relay is where im suppose to connect my “c” wire on the boiler side. I have 18/5 wire ran already. Just need to find out where to terminate. To the ...
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1answer
329 views

Connecting Wood/Electric Furnace to Smart Thermostat

UPDATE: I spoke with an ecobee tech and they pointed me to an alternative solution. If I get an adapter called a "Fast-Stat Common Maker", all I need to do is figure out where to connect the C-Wire ...
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1answer
76 views

Weathertron Xl1200 to Nest Thermostat

We have a Trane Weathertron Xl1200 heating pump with the thermostat pictured below and are trying to replace it with our new Nest thermostat. Our old system has a variable speed air handler and we ...
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6answers
736 views

Why can I not find a 120V programmable 2-pole thermostat

I'm wanting to connect a 120V wall heater to a programmable, 2-pole thermostat. The difference between 1 vs. 2 poles involves whether or not the thermostat can truly, completely cut power or not. ...
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1answer
89 views

Ecobee 3 lite Installation — Confusion about C wire (on furnace but not at thuermostat)

I am about to install the ecobee 3 lite thermostat. On the thermostat end, there is no C wire - just the typical 4 wires - R,Y,W,... On the furnace end though, there is white C wire too, which I do ...
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1answer
960 views

C wire and smart thermostat (with pictures)

I'd like to install an ecobee3 thermostat, but I'm not entirely sure about my wiring. The current thermostat seems to only have a W and RC wire coming into it. There is also what appears to be a blue ...
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2answers
817 views

Installing thermostat - No C wire or C terminal available on furnace

So I've looked through many posts all over reddit and other websites but it seems every furnace is slightly different. I am an early twenties guy who doesn't want to burn down his apartment. If ...
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14k 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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2answers
76 views

Need a common wire

So, I recently moved. In my old place, I used my Nest without a common wire and never had an issue. However, in my new place, my Nest thermostat was working fine for about 20 days and started losing ...
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1answer
43 views

Try to rewire Nest and Furnace but Y is not used on Furnace

I installed a Nest at home and it worked OK. Recently, I noticed there was a power issue. Google and others suggested adding a power supply by using the existing G wire because there are only 4 wires. ...
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1answer
2k views

Hooking a wifi thermostat to a 2 wire boiler

I'm in the process of figuring out how to swap my existing thermostat for a new WiFi thermostat. Naturally it's connected to my home's boiler by 2 really old cloth wrapped wires. Examening the wires,...
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2answers
27 views

Thermostat settings two hvac units older house

So I purchased a historic house built in 1920. The house has two HVAC units, one for the upper floor, one for the lower. Total sq ft 3300. I had been setting the upstairs thermostat at about 83 ...
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1answer
179 views

How to connect wifi thermostat with a boiler after cable upgrade?

I have an old battery operated thermostat right now with two wires (18/2) attached to it running to a boiler. No AC, fan, etc.-- just a boiler. I can easily replace the wire with 18/5 one, however I'm ...
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1answer
754 views

How to install a 4-wire a/c & fan thermostat with only 3 wires

My home currently has a central a/c unit which is controlled from an 3-wire old mercury switch thermostat. I want to replace it with a newer Honeywell that requires 4 wires. The existing thermostat ...
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1answer
2k views

How to wire C wire to the transformer of HVAC?

How are you all doing? I tried to connect the digital thermostat (Ecobee3) instead of my old honeywell thermostat. The original wiring is below (figure 1) HVAC is located on the ceiling of bathroom ...
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1answer
664 views

Can I run a C wire from Fan Relay

We've just moved into a new home with an heat only, oil, forced hot air furnace. The current thermostats are very old and we'd like to update them to something like a nest. The furnace is currently ...
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1answer
245 views

Old Thermostat with just R and Y wires?

UPDATE: this may be R and V, not R and Y, although I'm still not sure how it was set up. I am replacing an old thermostat in my house (the house is from the 60s, I'm not sure how old the thermostat ...
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1answer
141 views

Smart Thermostat and 24 volt transformer direct to thermostat

I have a hot water boiler and separate AC system and bought a wifi smart honeywell thermostat to get a C wire- installed a 24 volt transformer that has two wires if one goes to the C where should the ...
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3answers
30k 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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1answer
975 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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2answers
3k views

Installing Nest 3rd generation thermostat from Old Trane Weathertron Thermostat (Mercury one)

Nest is not detecting Power (Rh) Showing error that power is not connected. Please help. Installing Nest 3rd generation thermostat from Old Trane Weathertron Thermostat (Mercury one) New stat wiring:...
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3k views

Nest thermostat - combi boiler and UFH set up question

We recently had some work done, a new open plan room, a new boiler and underfloor heating (UFH) put in. We had some confusion, a lot of which comes from not having a basic understanding of how the ...
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1answer
231 views

Replacing old thermostat with 2 white wires for zone boiler heat

I am replacing our basement thermostat that had a white and orange wire together and a white and blue wire together. That is all there is. I ham trying to put in a heat only non programmable honeywell ...
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1answer
64 views

Furnace and Thermostat Issue

One day my parent's furnace and thermostat stopped working. The thermostat is a smart thermostat that depends on 24volts to the R and C wire. We measured voltage between the R and C wire and was ...