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What to do When a Thermostat’s Red Light Blinks or Stays on

What does it mean when your thermostat is blinking a red light.

When the thermostat Emergency Heat Light is flashing or on during normal operation (whether in the cooling or the heating mode, but not the Emergency Heat mode), this typically indicates that the outdoor unit is “locked-out”. This means the outdoor unit has shut itself down because of a problem, and it sends a signal to the thermostat, letting you know that there is a problem with the unit. When this happens, the indoor unit tends to keep on running because the indoor unit doesn’t know there is a problem. And if the outdoor unit isn’t running, the indoor unit will most likely never satisfy the thermostat; it will just keep running and running and running.

Numerous systems, like the York Stellar Series units, have a diagnostic feature. When you see the light flashing, it flashes a code. You can count the amount of flashes, usually between two and nine, and then it just repeats itself. You can then reset the system by turning the thermostat “off” and waiting 30 seconds then turning it back “on” again. This should restart the system, but it may take up to 10 minutes for the outdoor unit to start up.

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What does it mean when your thermostat is blinking a red light.

Some systems need shutting the power to the indoor unit off momentarily, and then back on. The light should also go out. After 10 minutes, see if the outdoor unit is running. If the light doesn’t go out or if the unit doesn’t start, you may need to call for service, assuming you checked for the obvious; like tripped breakers or the outdoor reset button.

At times, a unit will “lock-out” on a fluke or a weather-related condition, and resetting it will resolve the problem. But if the unit “locks-out” again, most likely there is an issue and you should schedule a service-call.

Below is a list of possible causes. All of the indicators for the York Stellar Series should be handled by an HVAC professional.

York Stellar Series Flash Code:

  • 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

Other Heat Pump Systems:

The first three should be handled by an HVAC professional; the last two can be handled by a homeowner.

  • High pressure or high temperature switch open
  • Low pressure or low temperature switch open
  • Defrosting too much
  • High pressure switch open – some units have a manual reset button located on the outdoor unit – possible cause: blocked air filter or coil, bad fan motor, overcharge, running heat on a hot day, stuck contactor in heating mode
  • Defrosting too much (weather conditions related) – potential causes: outdoor unit in a snow-drift or covered in ice.

If you need help maintaining your thermostat or other part of your heating system in your Chicago area home, call American Weathermakers at (847) 503-9497 today to learn more about what we can do for you.

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