No one likes it when on a cold night, there isn't enough heat or maybe no heat at all coming from the furnace. While a qualified service technician may be needed to make most furnace repairs, there are some common heating problems that a homeowner may be able to diagnose before placing that service call. Whether you have a forced hot air or hot water heating system, if your furnace doesn't seem to be working, it helps to be aware of some of the things that can go wrong.
Make sure the thermostat is on the "heat" setting rather than the "cool" or "auto" position. Set the temperature on the thermostat a few degrees higher than the temperature in the room. If a thermostat isn't set above room temperature, the heat will have no reason to come on.
Check for an electrical problem. Locate the power switch on or near the furnace to make sure that it is in the ON position. Switches not located on the furnace are often located somewhere near the basement stairs. If the power switch isn't the problem, you may need to reset a tripped circuit breaker in the service panel box. The box usually hangs in the basement on the wall near where the electric meter is located on the outside of the house. Move the switch on the breaker supplying current to the furnace all the way to the OFF position before moving it back to ON in order to restore power. The switch should be labeled. A good rule of thumb is to wire a furnace into a circuit of its own to prevent overloading the circuit.
Press the "red" safety reset button. The electric motors on most heating systems have an overload reset button that pops out when the motor overheats, shutting down the furnace. When the motor has had time to cool completely, you can manually restart the furnace by pressing the red button back down again. If the button won't reset within 60 seconds, or the furnace turns off again after resetting, call a service technician. The reset button may be yellow on some models of furnaces.
Confirm the fuel supply to the furnace. Make sure the gas is turned on if you have a natural gas furnace. The gas valve should be turned all the way to the "open" position. For a furnace that uses liquid propane, make sure that the tank hasn't gone empty. The gauge attached to the tank looks like a round dial. If you have an oil furnace, check the gauge, which is usually located on the top or side of the oil tank.
Replace the furnace filter if you have a forced air heating system. A dirty or clogged filter reduces the heating efficiency of a furnace. You should clean the filter at least every three weeks throughout the heating season, and change it every three months. Fiberglass filters should be changed monthly. If the filter looks gray and dirty when you remove it to clean, it's definitely time to change to a new one.