IF you hear clicking sound (spark electrode firing) then motor is running, sail switch has made up and power has reached circuit board (spark electrode won't fire otherwise)
Need to check IF gas valve is getting power and/or if gas valve solenoids are working.
Power goes to gas valve solenoids at same time power goes to spark electrode
(Power on gas valve solenoids for 6-8 seconds during spark electrode firing)
Problem could be faulty solenoids on gas valve
OR obstruction/blockage in main flame orifice---burner tube
OR dirty/obstructed burner
OR misaligned spark electrode
That vintage (old) of furnace probably could use a through cleaning
