What Does A Thermostat Red Blinking Light Mean?

You notice a thermostat red blinking light. If you look closely, the red light will flash a number of times and then pause for a second. What does this mean? If you see the red flashing light during regular operation, this usually means that the outdoor unit was shut off due to a problem and is currently “locked out” from normal operation.

When you see the red flashing light, it is usually in a diagnostic feature to alert the HVAC repair technician to what the problem is. Generally the code is between two and nine and it will keep repeating the flashing code. Occasionally this warning may be triggered by warm weather conditions and resetting the system can solve the problem. If not, service may be required for your system.

Reset your system by turning your thermostat “off” for at least 30 seconds and then turn it back “on.” This should restart the system, but it may take some time before the system resumes operation. Wait at least 10 minutes and check if the outdoor unit is running. If the light doesn’t go out or the outdoor unit does not restart then there is an issue that will require a HVAC service technician.

What are the possible causes for the red flashing light?

  • 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

Contact your local certified HVAC repair technician for a heat pump repair or an Air Conditioning Repair to diagnose and repair the problem.