The furnace turns on, When blower starts in "auto", it shuts off after 5 secounds, but when the fan in in the "on" position, & the furnace runs fine. The fan runs all the time as it should in the on position. Try a new themostat? thanks, Kevin
When the fan switch is in auto, it shouldn't run unless the furnace is on. With the fan switch in the on position, it should run constantly.
Does the fan turn on while the furnace burners are lit?
Or does it stay off when the burners are on?
What brand/model furnace do you have?