Four technical reasons – and one housekeeping reason – are likely causes if your furnace stops working properly.

The non-technical one is an easy fix: The filters need cleaning or replacement. Filters capture ash and other debris; if the detritus isn’t removed periodically it can build up enough to slow or stop the furnace’s operation.

A homeowner or handyman can do this. Indeed, dirty filters are the first suspect in many problems involving all sorts of heating and cooling equipment.

The other likely reasons for furnace failure will require an experienced technician:

Worst-case scenario

The heat exchanger is expensive and important. It’s key to providing heat to your home or business, and it controls carbon monoxide and other poisonous gasses, making it a vital safety asset, too.

A crack or other snafu can shut down the heat exchanger. Then you have the option of repairing it or buying a new furnace. This will depend on the current system’s age and dependability.

In either event, call a technician asap to make sure there’s no chance of toxic gas escaping.

Ignition

Ignitions sometimes fail, which means no more heat.
An annual maintenance check should include a good examination of the ignition system to determine if it is weakening.

Fan Assembly

A blow fan assembly clogged with dirt also can shut down a furnace. A simple dusting by the homeowner isn’t enough. The system is complicated by bearings, belts, pulleys and fan motors, so a technician is best suited for this delicate task.

Again, this is an area that should be examined as part of an annual maintenance check.

Furnace thermometer

Like other instruments, the furnace thermometer can wear out or lose calibration, which will cause the furnace to turn on too often or not at all.

Premier HVAC repairs and installs furnaces in Manhattan, Brooklyn, Queens and Long Island.