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

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AC Unit does not receive 24 volts on outside unit

My outside unit does not turn on itself, but it does work. I just did a quick repair just thinking it was the capacitor and it was only 15 dollars for a new one so I changed that out and still had the ...
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1answer
15 views

HVAC compressor turns on when calling for fan only

I just moved into a new apartment with HVAC, and I'm looking to control the thermostat with a few Phidgets (I had already invested in that ecosystem, so I just needed a couple of relays). Anyway, ...
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53 views

How do I connect a honeywell wifi thermostat with no C wire at the furnace?

I purchased a Trane XV90 furnace in 2001 & I'm upgrading the thermostat to a Wi-Fi model. This thermostat needs a wire labeled C from the furnace & of the 4 wires coming from the furnace none ...
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1answer
59 views

Central Air Unit not Sending Enough Power to Thermostat

Right now I don't have specifics on my central air unit (make, model, etc) but hopefully the info I provide will help. I have a Second Generation (and Third Generation) Nest Thermostat hooked up to ...
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1answer
24 views

One thermostat with a switch to control 2 heating systems

I have a natural gas boiler and a pellet stove. I have a Honeywell programmable thermostat (2 AAA Batteries) that I have used independently with both of these systems. Switching from one system to the ...
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2answers
48 views

How do RH/RC/R and Y/W relate for HVAC?

I have the following notes for HVAC (that I've compiled from reading through here): Thermostat wiring: C low voltage power wire that brings power from heating/cooling equipment to thermostat ...
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1answer
34 views

What could be causing my Thermostat “R” wire to only be 8 VAC?

I am trying to install a Nest thermostat. It says Rh not powered. I checked with a meter and I get approx 8 VAC reading. What could be causing this? The furnace itself ain't pretty. Update: ...
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11 views

AC electronic thermostat went black

I have a new (2013) Lennox AC unit. There is an electronic thermostat that just went black a few days ago. This has never happened before as, even when the AC is off for the winter, the thermostat ...
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1answer
16 views

12 gauge on 30 amp circuit - after thermostat

I have 2 2500 watt baseboard heaters that I'm planning on running off of a 30a 240v breaker. My question is, because the thermostat is close to the panel, can I run the 10/2 JUST to the thermostat, ...
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2answers
47 views

Why does my heating work poorly in moderately cold temperatures?

My house has a gas-fired boiler and hot-water radiators. I've noticed a strange problem since moving in a few months ago. If the weather is moderately cold (in the 30F - 40F range), my house feels ...
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1answer
26 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
33 views

Temperature of water in the shower fluctuates - will a cheap thermostatic tap help?

I recently moved to an apartment where temperature of water in the shower fluctuates and we called for a plumber. He either cleaned up or replaced one part (I think it was the mixer - nothing visually ...
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1answer
35 views

Does thermostat need to be grounded?

If a thermostat is connected to an air handler, which is connected to the main panel and has a ground wire, should one of the thermostat wires be connected to the ground?
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24 views

Thermostat replacement in a double wide

We have a new double wide and I want to replace the thermostat with a new programmable one. We took off the old one and it has 3 red wires, 2 yellow, 1 white and 1 green. I get the 2 red indicate a ...
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1answer
20 views

New thermostat for electric radiant ceiling heat

I live in the Pacific NW where radiant ceiling heat is common in older homes. I a have home built in 1969 and want to upgrade the thermostat to something newer that we can program and save money. This ...
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1answer
96 views

How can I connect a WIFI thermostat to a Honeywell R845A switching relay?

I'm trying to install a wifi thermostat and it won't power up. The old thermo was battery operated 2 wire but there were spare wires. At the R845A relay, red and white whites connect to terminals 5 ...
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35 views

Installing Honeywell wifi thermostat - weird wiring

I bought a Honeywell 7 day programmable wifi thermostat (non touch screen model). My old thermostat was wired as: Red - rh & rc Blue - b Green - g White - w I also have an unused blue wire (not ...
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1answer
129 views

How do I wire a thermostat with an external 24v transformer?

My current wiring has 5 wires, R, Rc, Y, G, and W wires. No C wire. I've added and external 24v transformer and connected one wire to the C connector but don't know what to do with the other. If I ...
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41 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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2answers
22 views

My furnace has a vibration for about a second at the end of the heat cycle.

It runs fine for the approximately 15 minute heat cycle. It appears as though it happens as the thermostat is satisfied and the gas valve shuts off. The vibration is heard upstairs and throughout the ...
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1answer
26 views

Stove Temperature Control broken

I have a (Simpson Mercury) electric stove - and 2 of the 4 elements do not work properly. They heat up, but it is not possible to set the appropriate temperature for them - they are either on or off. ...
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1answer
35 views

Vent now blows on thermostat

A long story how this got this way but there's a house with two furnaces and two thermostats. One of the furnaces feeds a long hallway with the return vent at one end and four feeder vents evenly ...
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1answer
415 views

Controlling 110v swamp cooler using Nest thermostat

I currently have an HVAC system that is connected to a Nest thermostat (2nd generation) and I'm planning to use the same Nest thermostat to control a 110 swamp cooler that is currently not connected. ...
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13 views

WiFi thermostat won't run. Not sure where to connect C wire [duplicate]

I just replaced a 2 wire thermostat with a wifi one that required a c wire. There was an unused blue wire which I attached to the C connector on the transformer at the furnace. At the thermostat, the ...
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380 views

Honeywell WiFi thermostat newly installed--not working

I just replaced a 2 wire thermostat with a wifi one that required a c wire. There was an unused blue wire which I attached to the C connector on the transformer at the furnace. At the thermostat, the ...
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1answer
53 views

Wiring for New Thermostat

I just bought new programmable z-wave thermostats (Honeywell TH8320ZW). I thought I had the wired correctly, but I woke up to a pretty chilly house this morning. The fan is working, but it seems to ...
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2answers
68 views

What's the name of this kind of valve?

I would like to install the smart radiator thermostat from my previous apartment: However, in the new apartment there are different kind of valves, with clamps, as seen here: Does anyone know ...
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1answer
38 views

How do I turn off the power to my thermostat?

I'd like to replace my thermostat with a new one. My current thermostat is one that doesn't have a C-wire and is powered by batteries. Now, my question is... is there a switch for the power that I ...
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1answer
119 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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35 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
37 views

Why would a 240v line voltage thermostat have a blank display?

In a bathroom I have a single 500w 240v electric baseboard heater, and AUBE/Honeywell TH305 digital line voltage single pole thermostat. I noticed yesterday, that the display had gone blank. A quick ...
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1answer
36 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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267 views

Can I connect the R and C wires directly to the HVAC transformer?

I have a Rheem furnace and a Ecobee3 smart thermostat. I'm having a problem where the Ecobee3 randomly loses power and reboots. I've traced this back to the control board (IFC) inside the HVAC unit. I ...
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87 views

Connecting a light-switch to turn thermostat on/off? (re: basement heat)

Is it possible to connect a simple light-switch to a thermostat? I'd like to have a thermostat in my basement set to 72 degrees. However, I want it completely turned off most of the time. I was ...
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44 views

Which Transformer for 220v to 24VAC for Heating Smart Thermostat

I have a 220V electric baseboard heating system which is controlled by a 24 VAC 2 wire thermostat (RH, W). There is a 220V to 24VAC relay in the circuit from the thermostat to the heating system. I ...
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1answer
36 views

Water heater pilot not staying lit

A customers 70 gallon gas fueled Bradford White water heaters' pilot light goes out immediately after releasing the red pilot button when relighting it. I concluded (in order of most likely suspects) ...
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1answer
70 views

How to power Honeywell wifi thermostat with external transformer

I want to install A Honeywell RTH 6580 WF thermostat in my garage for heat only . My heater is a simple LP gas, hanging unit heater; heat only and my thermostat has two wires labeled W and R . I ...
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2answers
46 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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53 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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2answers
109 views

Confused by ~115VAC 5-wire cabling to UK thermostat

I have a 5-wire cable as used for 3-phase (i.e. stripes/blue/brown/black/grey) coming to a hole where a thermostat was - only the earth, live (brown), and switched live (black) were used by this ...
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16 views

Possible of override 2 zones with one thermostat

I have a vacation home with 2 zone heating. In the winter, it would be nice to be able to have remote access to the thermostat and 'turn on the heat'. Normally when vacant the 2 zones will be set to ...
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2answers
122 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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2answers
62 views

Cost of adjusting the thermostat

Is it more cost effective to (1) play with the thermostat by lowering it at times that you're not home or needing the heat and raising it back later or (2) leaving the temperature on a set amount and ...
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1answer
113 views

How to hook up C wire to Crown air handler

Sorry for the newbie question, but I would like to hook up a C wire so that I can get a Nest, Ecobee, etc. My current thermostat is just a regular battery operated Honeywell and looking at the ...
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1answer
32 views

Can I add a slave to existing thermostat?

The bedrooms in my condominium looks something like this: A common HVAC unit provides heat and air conditioning between bedrooms, with the thermostat being in the Master BR. Problem: Bedroom 2 ...
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1answer
52 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
283 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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1answer
65 views

1 nest to control all vales on UFH manifold?

We are having an extension done and intend on having all underfloor heating in the new area. Currently we have a valiant combi boiler supplying the main house which has been T'd off with a valve for ...
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1answer
54 views

How to wire programmable thermostat that doesn't have an E termimal

I am trying to replace a manual with programmable thermostat that is missing emergency heat (E) terminal. There are bits and pieces of information I have gathered but am still not clear. Can I leave ...
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1answer
32 views

How to simply turn heating on/off with VRT 340f thermostat?

I've just moved into a new house and it has a Valiant boiler with a VRT 340f thermostat and I have to say it is completely perplexing even after having read the manual several times! It seems ...