A: There can be any number of reasons why your furnace is not heating. We’ve collected the most common ones below, but be advised that testing some of these hypotheses will require the aid of a qualified professional, plus the purchase of furnace repair parts. The parts that might be causing you trouble have been listed in order of how commonly they occur, starting with the most troublesome ones. We’ve also added some less than ideal situations in which your furnace might break down to the point where it’s no longer heating your home.
The igniter that’s supposed to light up the gas flame is not working properly. All furnace igniters have 120 volts running through them, provided by the main control board of the heating unit. When it does work, it’s lit up to the point where it starts glowing a bright hue of orange. A cracked or faulty igniter will need to be replaced.
The flame sensor that’s in charge with monitoring the gas burner is failing to properly detect the flame. This, in turn, will cause the control board to stop supplying the gas valve with power, hence bringing ignition to a screeching halt. Try cleaning up the flame sensor with an abrasive material (nothing too harsh) before you consider replacing it. If the problem repeats itself, then you’re definitely going to have to buy a new flame sensor.
When it breaks down or malfunctions due to shoddy manufacturing, the draft induction motor of the furnace stops properly drawing air inside the burner unit. Under normal circumstances, the air brought inside the unit would then go out through the flue of the furnace. There’s also a pressure switch inside the burner unit, which this flow of air needs to close down, in order to indicate to the main control board that air is flowing through the heating system the way it’s supposed to. Without auctioning the switch, the ignition process will fail to start or be delayed.
Most problems that require furnace repair parts and professional assistance boil down to a single issue: ignition is not occurring the way it should be. If the control board of the furnace is at fault, then you’ll absolutely have to get a new one, since fixing them is a very complicated process. A control board that’s not working well will fail to power all the other components involved in the ignition process with the voltage they require.
There are several switches inside a furnace heater and this one is in charge with making sure the heat around the burners is being properly regulated. Normally, the flames from the burner should be led into the heat exchanger and exhausted out through the flue. When the roll-out switch is malfunctioning, it will fail to properly acknowledge this process, open, and stop the heating process inside the furnace. This is most often caused by the fact that the furnace is placed in a room where there’s not enough air, or because one of its exhaust vents is jammed. Before splurging on furnace repair parts, always check out if your vents and registers aren’t being obstructed by rugs, furniture, or other items.
Make sure that all the contacts inside your wall thermostat are working properly. If they’re not, then there’s no way your furnace could heat your house the way you want it to.
During ignition, the main control board of the furnace sends 24 volts into the gas valve assembly. If that valve isn’t working well, then it won’t open the way it should, hence not allowing gas to flow inside the burners. First off, you will need to make sure the problem doesn’t lie with the control board, as outlined above. But if there’s proper power flowing through the valve, yet it still fails to open, then that’s your culprit right there.
During draft induction, air flows through the furnace burner; at the end of this process, a pressure switched is flipped, indicating to the main control board that the air is flowing properly through the burner. Subsequently, ignition will be initiated and the furnace will heat up. If the pressure switch won’t close, then there’s no way the furnace can ignite the flame.
Aside from all the above scenarios, make sure the furnace is being properly supplied with all it needs in order to work well. Here are some of the most common supply-related situations that could be causing your furnace to malfunction: