My furnace won’t turn on! How can I troubleshoot?

The most common causes of your furnace not turning on or not heating are:

1. No power to your furnace: Check the furnace breaker switch at the main breaker panel. If the breaker has been tripped, try switching it back on.

2. The furnace is overheating: All furnaces contain an internal temperature sensor that serves as a safety mechanism. If your furnace overheats, this sensor will trip, causing the heat to turn off. The furnace may continue to run the fan blower to help cool itself off, or may not carry out any function until the system is reset or has cooled down sufficiently.

Furnaces commonly overheat as a result of the following conditions:

  • Running for long periods: The colder it is outside, the harder and longer your furnace will run to keep the inside of your home warm. In some cases, this can cause overheating of your furnace unit. Lowering your heat temperature set point may help prevent your furnace system from overheating.
  • Reduced airflow: Clogged or dirty air filters reduce the airflow through the furnace, which can cause it to overheat. Check your filter. If the filter is clogged, it should be replaced or cleaned.

If your filter is clean or was recently changed, there could be a build up of dirt on other elements in the furnace like the condensing coil or heat exchanger.  If changing or cleaning the filter does not resolve the high limit switch problem a technician may need to do a deep clean.

3. The thermostat is not calling for heat: Your ecobee thermostat will display a flame icon with an orange colored outline when it's calling for heat. If the outline on the flame icon is white, the thermostat is not calling for heat.

heating.PNG       notheating.PNG     
Calling for heat       Not calling for heat      

By default, the ecobee will engage your heating when the indoor temperature drops 0.5 °F (0.3 °C) below your heat set point. This is called the "heat differential temperature". If the indoor temperature has not dropped below the heat differential temperature, the ecobee will not call for heat. You can learn more about the heat differential temperature, including how to adjust it, by visiting Threshold settings for ecobee thermostats (ecobee3, ecobee3 lite, ecobee4)

If the outline on the flame icon on your ecobee thermostat is orange, but your furnace is not heating, or if any of the other scenarios explained above do not apply, please reach out to us for help troubleshooting the issue.

Note: ecobee thermostats require a constant 24VAC power supply from your furnace to operate. If your ecobee thermostat has powered off it is likely not receiving any power from your furnace. If your ecobee thermostat is frequently rebooting then the furnace is also likely to be the cause.



Was this article helpful?