If your furnace quits or malfunctions, try these solutions before you pay for a $200 service call.
Make Sure Thermostat is On
Turn the setting to "heat" and check the temperature setting. Compare the temperature to the room temp. Set the thermostat higher so the furnace kicks on. Also make sure the time is right, and replace the battery if needed.
Check Shutoff Switches and Breakers
Look for the standard wall switch on or near the furnace. Check the circuit breaker or fuse for the furnace. Make sure the front panel covering the blower motor is secure.
If the blower is running but no heat is coming out, replace the filter. Make sure the furnace is off. Refer to your owner's manual on how to remove it.
Make Sure the Gas is on
Just like the switches, someone may have turned off a gas valve and forgot to turn it back on. Trace the gas line back from the furnace, and turn the handle so it's parallel to the pipe.
Flush out Drain Lines
High-efficiency furnaces can drain off several gallons of water daily in heating season. Remove the hose if needed, and fill it with 25% bleach / 75% water, then flush it and reassemble.
Make Sure Chimney is Clear
Turn the furnace off and the thermostat down, then dismantle the duct where it exits the furnace and remove any debris. Then reassemble the duct.
Look for blocked or leaky ducts
If only a limited number of rooms are cold, make sure the registers are open. Then examine the ductwork and seal any gaps between sections with metal duct tape. Open any handles protruding from the ductwork.
Clean Away Debris from Heat Pumps or Intake Vents
If you have a furnace that vents out of the side of your house, make sure nothing's blocking it. If you have a heat pump, clear away grass and leaves from the fins of the outdoor compressor.