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Home Thermostat Troubleshooting & Repairs

©Don Vandervort, HomeTips

With many electronic thermostats, you pull the body straight out from the baseplate to remove it for access to batteries.

Many problems with a heating or cooling system can be traced back to the thermostat. In some cases, the thermostat is out of adjustment. Other times its batteries are dead. Obviously, replacing batteries or making a simple adjustment are easy solutions.

If your electronic thermostat is acting up and you’re sure it’s programmed properly, replace the batteries. With most types, you pull the thermostat’s body straight out from its baseplate and find the batteries mounted to the back side of the body. But check your owner’s manual…if your thermostat isn’t built this way, you’ll break it!

If these steps don’t do the trick and your thermostat is outdated, it may not be worth the time and effort to fix it. It may be more affordable and sensible to replace it. Please see Home Thermostats Buying Guide. Then, for information on how to install it, see How to Install or Replace a Thermostat.

Thermostat Doesn’t Control Temperature

When your thermostat says one temperature and you know the room is another, it may be dirty, tilted on the wall, or located where it can’t get a proper reading.


1Turn the power off to the heating system.


2Remove the thermostat’s cover. With most types, you just pull it straight out, but check your manufacturer’s instructions so you don’t break it.


3Use a soft brush or vacuum with a brush attachment to gently and carefully remove dust and dirt. If the thermostat has two parallel metal strips, wipe them off with a soft cloth.

4Look for corrosion. You can try to remove corrosion with electronic contact cleaner. If it’s an outdated thermostat, consider replacing it with a newer model.

5If you have a mechanical (not electronic/ programmable) thermostat, be sure it is mounted level on the wall. Check it with a small torpedo level.

6A thermostat should be mounted about 5 feet from the floor, located where it can easily sense an air sample that is consistent with room temperatures. This means it should not be put in a corner, behind a door, in a closet, near a window or door, or near a heat source. If it is mounted in one of these spots, consider relocating it. This involves rerouting wires so unless you’re handy with this sort of thing it’s probably better to hire an electrical contractor or heating technician to do the work.

7If none of these steps works, replace the thermostat with a new programmable thermostat.

Extreme Temperature Swings

If your gas- or oil-burning furnace cycles on and off too frequently or there are major swings in room temperature before the furnace goes on, the thermostat may just need a simple adjustment. To adjust the thermostat:

1Remove the thermostat’s cover. For a mechanical thermostat with a mercury switch (a small vial filled with mercury), first use a small torpedo level to make sure the thermostat is mounted level on the wall. If it isn’t level, it won’t measure temperatures properly.

2Adjust the heat anticipator. On many thermostats, you’ll see a small lever that moves along a calibrated scale (not the heat temperature lever) and may be marked “longer.” This is the heat-anticipator adjustment. Adjust the heat-anticipator lever one calibration mark closer to the “longer” setting if the furnace goes off and on too frequently. If the furnace allows room temperature to drop too low or rise too high before the furnace goes on or off, move the lever one mark away.

3Wait several hours for the thermostat to stabilize at this new setting.


4Repeat the adjustment if necessary.


5If making these adjustments doesn’t solve the problem, consider replacing your thermostat.

mechanical and digital thermostats©Don Vandervort, HomeTips

If your thermostat can’t be repaired easily, buy a new one!
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  • Buster666

    Is there an adjustable thermostat on the outside unit on a heat pump?

    • Don Vandervort, HomeTips

      No, the interior thermostat controls the system.

  • Alfredo Cardenas

    My forced air space heater keeps constantly cycling. When the thermostat calls for heat, the burner goes on . After a while the fan goes on (as it should). But when the fan goes on the burner goes off. A few seconds later the fan will go off and the burner will go on and they continue to alternate with them never being on at the same time. What gives?

    • Frank Fletcher-Broucek

      Move the fan limit switch to 105 deg. and the heat lmit to 140 deg.

  • Miss Deborah

    I have never had a heat pump before, didn’t even want to move into an apartment because of not being in control of my temperature, But I tried it out,in some apartments but forgot that when I moved in the first thing one of my neighbors told me was to go an buy a window ac unit, thank God, Now I have moved in a townhouse , an I forgot what that neighbor so long ago told me an I need help. about three months ago I noticed that the fuse would trip every time I turned the ac to about 65,but it would run, last week it didn’t but it still took me a couple of days before I realized it wasn’t cooling at all. Changed the batteries, tried resetting the thermostat , no cold air at all. fan comes on an blows but no cool air, Whats next?

    • Frank Fletcher-Broucek

      You likely have a refrigerant leak. A service call would look for a leak and give you a recharge of the refrigerant. What was in the home inspection report?

  • Suzanne Campbell

    My emergancy heat pump on my electric heat an air unit is coming on at 70 degrees!!! Why???

  • Adrianne

    We have two thermostats – one upstairs and one downstairs to control each zone. The t-stat downstairs now supplies heat upstairs which we don’t like because since heat travels up, the upstairs becomes too hot. This suddenly happened two weeks ago and we don’t understand why. Any tips?

    • Frank Fletcher-Broucek

      Switch the upstairs signal wire with the downstairs wire at the furnace.

  • Debbie Hederson

    i got Bryant PA3Z-b unit in Feb.2014 it work fine but this morning my unit blowing out cool air not hot air why?

  • Big Al

    Do all electronic thermostats have batteries. I removed the thermostat cover and I did not see batteries. My heat pump does not come on. With the blower in the ON status on the thermostat the blower blows air. However the fan on the outside compressor/condenser unit does not turn and I get no heating. Could this still be a thermostat problem? It has three wires, how do I check if it is working? What else could it be?

  • Michelle Lee

    Just changed t-stat twice, assumed the 1st was faulty. Home stays heated properly for several hours, and then the furnace stops running and the temperature drops to about 54-56 degrees. I haven’t been home long enough, or been able to stand the cold long enough to see if it eventually turns back on, but I’m assuming it does not. When I go to the furnace and flip the switch back and forth on it, it turns back on and the house heats back up for several hours again……any suggestions?

  • A/c does not cut off when reaching desired temp. Keeps running and running. It seems the thermostat itself is generating heat which makes it keep running.

  • Sergio Garcia

    My AC does not turn off after it reaches desired setting how can I turn it off .

  • LaDonna Stephenson

    I set my thermostat to 71° and it stays 3° warmer at 74° . Is this normal or what is the problem. New AC unit and thermostat, first summer using it.

    • Gina Hall

      Thermostats have a protocol called hysteresis. This is a variance allowed by the software to save energy and wear and tear on the unit. Basically, most thermostats allow about a 3 degree variance. That means if you set your thermostat to 71, it won’t turn on AC unless it gets above 74, and won’t turn on the heat until it gets below 68. The reason is, if it didn’t have that variance, as soon as the thermostat was anything but 71 exactly (ie 70 or 72), the climate control would kick in. A momentary draft from a door could shift the temp 1 degree, which means the system would be constantly running and turning on/off.

  • Jamie Niehaus

    I recently had to change my tstat out. It was a fairly new one , however the display messed up and went out, I thought it was the batteries, however when I popped it off to replace them, water was dripping out! Not sure why or how.. Well the new one has been installed for 3 days now. And curious, I popped it off to see, and sure enough there were water drops in it again.. I live in an older trailer with no kind of insulation and the windows are paper thin.. and where the property owner moved the tstat, it is not even a foot from a window, could that be the reason for water? I also live in texas, so pretty hot temps outside.. I don’t want to end up having to get another tstat, if anyone has any ideas, id love input. I know it is the property manager responsibility to replace, however they take days to weeks to come out for any repair or maintenance ,and with the heat, I couldn’t take being inside my own home for days with no kind of air. Thanks in advance for any ideas of what it causing the water… I’m new to this site also, so if you have any ideas. Please send me a message on fb, or comment here but i may not see replies here. Thanks.

    • Gina Hall

      The water is probably condensation. When you’re outside in Texas, it’s hot and humid as hell. (How is God’s country hotter than hell?!) When air is drawn in and cooled, the humidity (ie steam) condenses to water. This is why the inside of a home is both cooler AND dryer than the outside.

  • tom

    i turned on my furnace and set it to 70 degrees and it still was on at 74 degrees so i shut it off is this normal for this to happen it wouldn’t turn furnace off

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