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4 Signs of a Faulty Thermostat

As we approach another cold New England winter, it’s imperative that your heating system’s thermostat is working properly so your family is comfortable all season long. In this month’s blog, the home comfort specialists at Main Stream Mechanical share four signs of a faulty thermostat and steps for testing your thermostat’s functiona

Indicators of a Faulty Thermostat

A thermostat is one of those appliances that we don’t pay much attention to until it breaks. Here are four warning signs your thermostat is failing:

  1. Unresponsive to changes in set temperature. If you adjust the set temperature and see no change in your home’s overall temperature, you may have a problem with your thermostat.

  2. Heat doesn’t turn on. If the wiring between the thermostat and the furnace/boiler is faulty, or if the thermostat is reading temperatures incorrectly, your heating system will not turn on. These symptoms require the expertise of an HVAC professional to assess the problem.

  3. Heat runs constantly. When your system runs constantly and won’t turn off, it could be a result of a frayed wire, or a mis-calibrated thermostat.

  4. Fluctuating temperatures. Temperature shifts occur when a thermostat switches the heating system on and off when it is not supposed to. When this happens, rooms that are furthest from the unit will not receive an even distribution of cool or hot air.

Thermostat Testing

Before replacing your thermostat, you can rule out common problems by performing several tests:

Check overrides. Check that your thermostat is in the AUTO position and that there are no programming overrides in place.

Change the batteries. If you change the batteries and the thermostat isn’t functioning or is unresponsive, contact an HVAC professional to troubleshoot the issue further.

Force a start. In heating mode, set the thermostat 10 degrees warmer. You should hear your thermostat click on as the system starts to run. Check the furnace/boiler to verify it’s on and operating.

Clean out dust. Open up the thermostat and check for dust or dirt buildup. Use canned air to clean out all the dust in and around the display and programming buttons.

Look for loose wires. Look for, but do not touch, any loose wires. If you see a loose wire, turn off the breaker to the thermostat, then reattach the wire. If you’re unsure about this step, contact a home comfort specialist, who can help.

Check the breakers. If neither your furnace nor your air conditioner turns on, check the breakers for each unit to make sure they haven’t tripped. If they are tripped, reset them, and check to see if the units are now running.

When to Call a Heating Professional

If your furnace or boiler still won’t turn on, the wire from the thermostat to the unit may be broken, or the heating unit itself may have an issue. A trained professional is needed to determine the problem.


Understanding the warning signs from your heating system gives you time to prepare for a repair or replacement. If your thermostat is broken or your home heating system is in need of maintenance or repair, contact Main Stream Mechanical’s home comfort specialists. We service many locations throughout Massachusetts and Southern New Hampshire, including Haverhill, Amesbury, Newburyport, Rowley, Topsfield, and Boxford.


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