Reasons for a furnace not working are a dirty filter, a faulty or a wrongly set thermostat and a closed gas valve. It can also fail to work if debris clogs the drain lines.Continue Reading
A dirty filter causes a furnace to run below optimum. It also causes the heat exchanger to overheat, causing the furnace to automatically shut. Inspect the filter every one to three months, and replace if dirty.
If the furnace is not blowing hot air when required, check if the thermostat is working. Set the temperature on the thermostat on "heat" and 5 degrees Fahrenheit above room temperature.
Check that the furnace is connected to a power supply. Look for a tripped breaker or a blown fuse, and ensure the gas valve is open and the pilot light is lit.
A furnace also fails if there is debris clogging the drain lines. Cleaning the drain restores the furnace to a working state.Learn more about Heating & Cooling