Why Does Thermostat Red Light Flashes Or Stays Lit?

Thermostat flashing red light is sign of outdoor unit being locked out. This means that outdoor unit is turned off automatically due to some problem. Signal sent is to the thermostat and the thermostat starts flashing the red light to tell us that there is the problem in the outdoor unit.

Even after the outdoor unit has stopped working indoor unit keeps on doing its job as the indoor unit is not aware that there is a problem. The unit will keep on running but will not be able to satisfy the thermostat.

Diagnostic features are provided in modern digital thermostat. The light on the thermostats flashes in a particular code. The light flashes from 2 to 9 times in a row and then repeats. Different code indicates the different problem in the system. This helps to identify the problem in the system easily and repair it without wasting much time in finding out the problem.

Some of the problems can be solved by just restarting the unit. Turn of the unit for ten minutes and turn it on again. The light should stop flashing the outdoor unit will start to work again. If the light does not stop flashing call the HVAC technician to look after the problem.

Different problem on different codes

• 2 code- off on high pressure
• 3 code- off on high discharge temperature
• 4 code- off on low discharge temperature
• 5 code- default defrost, defrosting too often
• 7 code- bad ambient sensor
• 8 code- bad liquid-line sensor

Here are the reasons why these problems do occur

• Blocked air filter
• Damaged fan motor
• Blocked air coil
• Running heater on hot day
• Outdoor unit covered with snow, leaves
• Overheated devise
• Low refrigerant




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