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 safety mechanism called a high-limit temperature sensor. If your furnace overheats, this sensor will trip, causing the heat to turn off. The furnace may 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.
- 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.
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.