What is and inducer and a pressure switch

See if this helps.

Inducer Fan Assembly.

The first thing a gas heating furnace does on a newer unit is it starts the inducer fan motor. The inducer fan motor is a small motor usually in the gas burner compartment, this small fan or blower is required to pull the hot gasses through the heat exchanger and it blows those gasses into the flue vent.

This inducer fan motor must be proven to be running properly usually with a safety pressure switch connected to the inducer fan blower housing with a small rubber tube, if the inducer fan motor is not proven on.

At this point the gas furnace heating unit will usually stop the inducer fan motor and may try the same sequence a couple more times after a time delay, if it continues to fail to run the heating unit will usually shut off and lock out.

This an be caused by a faulty pressure switch, a bad rubber tube or in some cases the inducer fan or blower itself is not working correctly or there is some sort of blockage in the gas vent flue.

Some older gas furnace heating units do not have an inducer fan and are natural draft units, most of these heating units have been replaced but there are a few still out there.

These heating units usually do not have a control board or have a much simpler version of a control board which is usually just a ignition control unit.


Not all Draft Inducer Fan Assemblies look alike, in this example you can see a very simple style of assembly with an open cooling fan in front. This particular assembly was removed from the blower housing and you can now see the blower wheel itself.

CAUTION - Always be very careful with electricity as it can be lethal, if you are not comfortable performing any of these steps please do not perform them, of course you are performing these steps at your own risk.

Important Note: The heating system control board is sometimes very sensitive to static electricity, avoid touching this board to prevent failure.