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7 Symptoms of A Bad Home Thermostat

A bad home thermostat can leave you without AC or Heating. This post was written to help our customers identify the most common thermostat issues.

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Because thermostats are mechanical/electronic devices, they are subject to failure. The average life cycle of a home thermostat is about 10 years.

1) Your Thermostat Has No Power

If your thermostat has no power, you will likely see nothing but a blank screen. Check to see if your thermostat is battery powered. If it is, a new battery may be all that is needed.

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Some thermostats get their power from a wired source. In this case, you would want to make certain the breaker for this circuit is flipped on.

2) The AC or Heater Will Not Turn On

When an AC or Heater will not turn on, the problem could be at the thermostat. First check to be sure the thermostat is set correctly to “Heat” or “Cool”.

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The fan setting should be placed in the “Auto” position. Finally, the set-point should be below room temperature for “Cool”. Or course, the opposite would apply for “Heat”.

3) AC or Heater Runs Constantly

An AC or Heater that runs constantly could be caused by a bad thermostat. It is the thermostat’s job to tell the HVAC Equipment when to run.
Most thermostats work similarly to a light switch. With this in mind, it is easy to see how the thermostat could get stuck in run mode after failure.

4) Room Temperature and Set Point Discrepancy

Differences in room temperature and set-point could be caused by a bad thermostat component. For example, a bad relay inside the thermostat could prevent the AC system from running.

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A bad thermostat relay can prevent system operation even with the thermostat’s program commanding the system to run. In this case, replacing the thermostat is usually the most affordable option.

5) System Constantly Cycling On and Off

If your AC System is constantly cycling on and off, the thermostat is usually the first suspect. This symptom is one that is best left to a trained AC Technician.
Loose wires, low batteries, incorrect settings, and un-calibrated sensors are just some of the things that can go wrong.

6) Thermostat Loses Saved Settings

Thermostats that regularly loose saved settings are likely suffering a power interruption problem. Again, loose wires, or low batteries are common causes.

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In extreme cases, the motherboard or memory are the problem. In this situation, replacement is the most cost-effective solution.

7) No Response To Set-point Changes

Normally, your home’s thermostat should respond to a 5 degree set-point change within 30 seconds. This delay could be much longer if you recently flipped the breaker on.
If there is still no response, check your fan (Set to “Auto”) and mode (Set to “Cool” or “Heat”) settings. Adjust the thermostat set-point up or down 5 degrees and wait 5 minutes.

When To Call In A Thermostat Professional?

It is usually time to call in the pros after all common-sense fixes have not worked. Our AC Technicians have the tools and experience to quickly find and repair any problem.


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Hiring a pro eliminates frustrating misdiagnosis, unnecessary expense, and possible DIY warranty issues. To get started, call our friendly Customer Service specialists right now!


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