2) Check Light switch on or near furnace. This is the main power to the unit. This switch being accidentally turned off is a very common service call.
1) Make sure your furnace air filter is clean. This filter is for air conditioning also. Too restrictive or dirty air filters account for the second largest group of service calls.
Click this text for important information on filters.
Click this text for important information on filters.
Before You Call For Service
4) Make sure you have your furnace doors on right. There is a door switch that kills the power to the unit if it is not on right.
3) Check the furnace breaker or fuse in main electrical panel. Air conditioning will have 2 fuses or a double wide breaker. Air conditioners also have a usually grey metal disconnect box by the outdoor unit. This box may or may not have 2 fuses in it. Conduit runs from this to the ac.
5) Hi-efficient furnaces (furnace that vents with plastic pipe) will have a drain system. Make sure it is not plugged. Carrier, Bryant, Payne drain trap is commonly plugged on 1994 - 2014 model. Click this text for video. Make sure vent pipes are not drifted over with snow or recirculating exaust back up into intake. This will frost over the intake and cause a pressure switch fault code.
6) A dirty flame sensor is the most common service call by far in the heating season. Every home owner should know how to clean one. YouTube "clean a flame sensor" if you are handy at all. The symptom would be the flames come on for a second or two, sometimes longer and shut off.