If your furnace is not heating, here are some reasons why furnace is not working. Caleb with One Hour Heating and Air Conditioning in Lee’s Summit, Missouri gives several possible reasons why your furnace not working.

If your furnace is not heating, check your thermostat first. Are the batteries dead? Is your thermostat set to heat?

One of the most common reasons to cause a furnace to stop working is a dirty filter.

Caleb gives some other possibilities such as a dirty flame sensor which is a common furnace problem. Most of these problems can be avoided with routine furnace maintenance and cleaning.

He also shares two stories of a very uncommon reasons why they’ve found a furnace not to work.