Must Know How
Calibrate thermostat temperature

Calibrate thermostat temperature

Air Conditioning

After some time, every thermostat needs a new calibration, otherwise it won’t show the right temperature in your home. Sometimes, the loss of calibration can be caused by dust or by an accidental blow. The loss of calibration can cause the temperature to rise or fall into your room.

This will not only affect the temperature but also the costs with house heating. It’s very important that you recalibrate your thermostat.

Materials Needed

  • Thermometer
  • Masking tape
  • Paper towels
  • Screwdriver
  • Soft brush
  • Spirit level

Before you start working on it, see what type your thermostat is: with magnetic contacts, mercury switch etc.

Checking the temperature

To check if the thermostat indicated the right temperature, use a house thermometer. Attach it to the wall with some duct tape, near the thermostat. Be sure that those two don’t touch and are set a few inches apart. Let them stay for 15 minutes and then read them both. See if the thermostat has the same temperature as the thermometer.


If you see a slight difference in temperature (a couple of degrees), then you should try and clean the thermostat. Dust can greatly influence the temperature as it can fill the stop the connections. Remove the thermostat cover and use a soft brush to remove the dust. Don’t use a vacuum cleaner as some circuits and wires may come off.

Recalibrating a screw thermometer

For calibration screws, use a wrench to keep the dial straight as you turn the screw. This can be found in the center of a curled piece of metal. Turn the screw on both sides until the contacts are open. Wait a few seconds and then close the contacts again. Test the temperature again.


Sometimes, a loss of calibration of mercury based thermostats can be caused by unleveled units. The mercury needs to be leveled in order to indicate the temperature correctly. Use spirit level and adjust the thermostat.

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