You notice a thermostat red blinking light.

Since thermostats, furnaces, and air conditioners can’t speak to you to tell you when there’s a problem, you have to pay close attention to the signals they do provide. Sometimes it’s easy: if your furnace short cycles frequently, for example, you know there’s an issue that needs to be inspected. So when you notice a blinking thermostat light, you should investigate the problem.

What Your Thermostat Is Trying to Tell You

If you notice a red light coming from your thermostat during regular operation, this usually means that the outdoor unit shut itself off due to a problem and is locked out from normal operation. When this happens, the outdoor unit sends a signal to the thermostat to let you know there is a problem with the unit.

The indoor unit, however, won’t know there’s a problem and will continue to run, but it will most likely never reach the desired temperature.

If you count the flashes, you may notice a consistent pattern. The number of flashes usually between two and nine indicates an error code. Sometimes you can fix the problem by resetting your system. Turn “off” your thermostat for at least 30 seconds, and then turn it back “on.” This should restart the system, but it may take a while before the thermostat resumes operation. After 10 minutes, see if your outdoor unit is running again and if the blinking red light has stopped. If not, you should call an HVAC repair technician from Bigham’s One Hour Heating and Air Conditioning.

You can also reset your thermostat by shutting off the power to the thermostat and outside unit waiting 30 seconds and then turning it back on. If your thermostat runs on batteries, changing out the batteries might also reset the system. Check your outside unit too for any obvious problems. 

It also doesn’t hurt to check your breaker box for any tripped breakers. 

Possible Causes for a Red Flashing Light

There are a couple of reasons why you might be seeing a red flashing light, and the number of red blinks could be a clue about what’s wrong. Common causes of a red flashing light include:

  • High Pressure or High Temperature Switch is On
  • Low Pressure or Low Temperature Switch is On
  • Low Discharge Temperature
  • Liquid Line Sensor Failed
  • Ambient Line Sensor Failed

If you have a heat pump, a blinking red light could indicate the unit is having problems defrosting. 

Fixes to Stop a Blinking Thermostat Light

Sometimes a red light means that the outdoor unit has shut down because weather conditions have disrupted it. This is common if you have the heat on during a hot day or snow accumulating around your unit. Since the outdoor unit has locked itself out of the system, it’s a good idea to check on it to ensure there are no obvious problems.

If you’ve restarted your system and you’re still experiencing a blinking thermostat light, your best bet is to call a heating and cooling technician to service your outdoor unit. 

Bigham’s Is Here to Help

Bigham’s One Hour Heating and Air Conditioning is the Bay Area’s reliable HVAC service team. We are on call 24/7 to service homeowners in San Jose, Santa Rosa, and Fairfield. Ignoring errors and problems from your HVAC system can lead to even bigger problems down the road, so it’s best to fix them as soon as you notice any signs. Call us today for a service appointment.