Nothing is worse than waking to a freezing, cold house to find that your furnace is not producing warm air. Your first inclination will likely be to call a repair service. But before doing this, you should troubleshoot your furnace; you may find that it's something simple you can repair yourself. This is the case whether you have a gas, electric or oil furnace. As always, refer to the owner's manual for your particular furnace.
Things You'll Need
Can of compressed air
Turn on your thermostat and set it to the heat position. Set the temperature higher than the current indoor temperature on the thermostat. Open the thermostat to see if the coils inside are clean. If there is dirt or dust on the coils, spray them with a can of compressed air.
Look in your circuit-breaker box to ensure that the furnace breaker hasn't tripped and is in the "on" position. If it has tripped, try turning off your furnace for about an hour. Then turn it back on. The furnace may have overloaded the breaker. If the breaker keeps tripping, it may need to be replaced.
Check your owner's manual for the location of the SSU switch on the furnace. Make sure the switch is turned on. If you have an oil furnace, look for a reset button. This turns the furnace on manually. Push the reset button a few times to see if the furnace will come on, but not more than this as you'll inject too much fuel into the furnace.
Inspect the air filter in the duct connected to your furnace. If it's clogged, it needs to be replaced. If your furnace is located near your dryer, the lint from the dryer may be clogging the filter. In this case, you'll need to change your filter more often.
Check your ductwork to see if any duct tape or connections are loose. You may have a leak from a duct. In this case, reapply duct tape or contact a repairman to fix the loose duct.
Place your hand against your air supply registers to ensure that air is flowing through them. Do the same with the air grilles where the heat comes out. Move any furniture or obstructions away from the air supply registers and the air grilles.
Call your local gas company immediately if you detect a gas smell. You may have a leak.