I have a Coleman home furnace with a white-rodgers circuit board,model 50a50-241.On occasion the blower would not turn off with the t-stat.I would lighly hit the side of the furnace and the blower would go off.Now the blower was stuck on and I found the start capacitor burnt badly and the circuit board constantly flashing indicating flame sensed no heat commanded.There is no flame and blower stuck on.I know I need a new capacitor but should I replace the circuit board for the malfunction?Also what would cause the capacitor to catch fire?The blower works fine.

Well a loose connection would cause that to happen, is the capacitor blown up? or just burnt terminals? I would start with replacing the cap, then see what happens, chances are, you have a relay sticking on the control board, and it may need to be replaced, if it continues to give false codes, replace it.