How to Troubleshoot Electronic Thermostats


A malfunctioning thermostat can cause headaches and cost money in energy bills. Before calling a professional to replace your thermostat, try troubleshooting it to see if you can identify the cause of the malfunction. By doing some detective work you may end up saving yourself some money.

Things You'll Need

  • Furnace filter
  • Furnace hoses
  • Screwdriver
  • Insulation
  • Painter's tape
  • Small paint brush
  • Rubbing alcohol
  • Cotton swab
  • Wire stripper
  • Look at the display on your electronic thermostat. Is it losing time? If so, the furnace may be hitting the high temperature limit or other safety limit that triggers a switch. The switch turns the furnace burners off and cuts the electrical power feed to the thermostat. When the power is turned off, the clock will stop and it will lose time. The high temperatures can be caused by a dirty filter or worn hoses. Replace the filter or hoses and see if that fixes the problem.

  • Check to see if the circuit breaker to the air handler of the heat and air conditioning unit has been turned off. If it has turn it back on.

  • Is the power display light not turning on? Look at the power switch near the the air handling unit to see if it has been accidentally turned off. This sometimes happens, as the power switch looks similar to a regular light switch. Turn it on if it has been switched off. If this doesn't turn the power display back on, open the thermostat by prying the lid off and look for batteries, which may be in their own compartment inside of the thermostat. Replace the batteries if any are found. The back-light should work now.

  • If you have a programmable thermostat, is it losing its program? Older electronic thermostat models do not come with batteries that keep the programming when the power goes out. Replace the old thermostat with a newer model that has a backup battery to prevent the frustration of having to constantly re-program it every time the power goes out.

  • Check to see if the thermostat has been installed in the right place in your home. The proper position for a thermostat is near the return where the filter is installed so that it can properly sense the temperature of the air that the furnace is receiving. If it is installed on a wall that receives direct sunlight or near a window or outside door it needs to be relocated. It should also be relocated if it is near anything that has a high heat gain or loss such as water pipes, heaters, fireplaces, and electrical devices.

  • Pry the thermostat off the wall, or remove the mounting screws, and check to see if the hole it has been installed in has a cold or hot draft moving through it. If the hole is large or drafty stuff some insulation into it and cover it with painter's tape to stop the drafts from hitting the thermostat's sensor.

  • Do some interior maintenance on the electronic thermostat. Turn off the power to the thermostat. Tighten the screws of the base and the terminal. Dust off the interior of the thermostat with a small brush. Sometimes dust can cause an electronic thermostat to malfunction. Clean off all of the small metal plates, called contacts. If they are corroded or dirty, remove the wires and gently clean the contacts with a small amount of rubbing alcohol on a cotton swab. Look at the wires that connect to the transformer located inside of the thermostat unit. If a wire is corroded, strip the wire of its insulation, cut off the corroded part of the wire, then reconnect it to the contact. Turn the power back on.

  • If your electronic thermostat is a wireless model, check to see if the batteries are lithium or alkaline. Alkaline batteries will die fast when installed in these types of models. Replace them with lithium batteries and the thermostat should run properly.

  • Test the transformer of the thermostat with a voltmeter. Probe all hot and neutral wires connected to the thermostat at their terminals to see if they are working. Tighten the screws on the contacts if they need it.

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