How to Calibrate Thermostat Temperature

A thermostat on a white background.
  • 1-3 hours
  • Intermediate
  • 0-100
What You'll Need
Masking tape
Paper towels
Soft brush
Spirit level

Your thermostat may lose calibration after a while, a situation which affects thermostat temperature. Loss of calibration can result from a number of things, such as accidental bumping and dirt. This can alter temperature so that a thermostat which is designed to warm a room to 70 degrees Fahrenheit might instead warm to only 67 degrees Fahrenheit, or too high to 73 degrees Fahrenheit. The former can make your home feel chilly even when the heaters are on, and the latter can raise your fuel bill by nearly 10 percent. In order to correct this problem, you will have to learn how to recalibrate a thermostat.

Step 1 - Pick a Method

Before you can recalibrate your thermostat, you will need to work out what type you have: One type of thermostat contains magnetic contacts and a calibration screw, and the other employs a mercury switch. This switch consists of a small tube which contains a silvery liquid — mercury.

Step 2 - Check the Thermostat Temperature

With your thermostat set to on, stick a thermometer to the wall a few inches away. (You can stick it to the wall with double-sided tape or masking tape.) You should place a towel between the thermometer and the wall in order to prevent them from touching. Try to ensure that neither thermostat nor thermometer is influenced by outside temperatures. After the thermostat has been working for around 15 minutes, compare the thermometer's reading with the thermostat temperature.

Step 3 - Clean Away Dirt

If you find a difference of more than 1 degree Fahrenheit, you will need to recalibrate the thermostat. First, check it to ensure that it is not dirty. Dirt can seriously affect the functions of a thermostat when the dirt becomes trapped between connections. To clean the device, remove the cover and clean around the edges and top of the thermostat. You should then brush around the connections. Do not vacuum, as this can cause the wires to come away from the terminals and will damage the thermostat in other ways.

Step 4 - Recalibrate a Screw Thermometer

If you have a calibration screw, you will need to use a wrench to keep the dial straight while you slowly turn the screw. You will find this screw in the center of a curved piece of thin metal. Turn the screw to the right and left until the contacts open. Remove the screwdriver, wait a second, and then reinsert the screwdriver and turn it until the switch's contacts close. Remove the wrench and try the heating again.

Step 5 - Use the Level

If the mercury-switch thermostat is still not functioning correctly, check that the body of the machine is completely level. The mercury needs to be level to function correctly. Check the straightness with a standard spirit level and adjust the thermostat if necessary. In order to get the machine to the correct level, you may loosen or tighten screws which connect the mounting plate of the thermostat. You can also turn the nut behind the bimetallic element. First adjust the thermostat to a cold temperature and leave it for 10 minutes. After that time, adjust the thermostat temperature to a normal heat and turn the nut again.

By following these easy steps you will ensure your thermostat temperature is calibrated correctly.