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Thermostat Repairs

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If these steps don’t do the trick and your thermostat is outdated, it may be more affordable and sensible to replace it. For information on how to do this, 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.

 

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 If it’s an outdated thermostat, consider replacing it with a newer model.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 bubble 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.

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 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.

Featured Resource: Find Local Thermostat Pros

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About Don Vandervort
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Don Vandervort developed his expertise more than 30 years ago as Building Editor for both Sunset Books and Home Magazine. He has written more than 30 home improvement books and countless magazine articles. He appeared regularly on HGTV’s “The Fix,” and served as MSN’s home expert. Don founded HomeTips in 1996.

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15 Comments

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

    Reply
    • No, the interior thermostat controls the system.

      Reply
  2. 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?

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

      Reply
  3. My Honeywell CT3200 MagicStat digital thermostat calls for heat when the temp reaches 53, even though the thermostat is set at 45. Does anyone know how (or if) this can be corrected?

    Reply
  4. 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?

    Reply
    • 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?

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

    Reply
  6. 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?

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

      Reply
  7. 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?

    Reply
  8. 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?

    Reply
  9. 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?

    Reply
  10. 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.

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

    Reply

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