Remedy

Ignition electrode short circuit

Adjust electrodes

Wide ignition electrode spacing

Adjust electrodes

Dirty and wet electrodes

Clean electrodes 

Cracked insulator

Replace insulator

Defective ignition transformer

Replace transformer

Defective automatic furnace controller

Replace controller

Burnt ignition cable

Replace cable; search for cause and eliminate

Pilot burner failure

Adjust ignition gas pressure

Ignition gas valve does not open

Search for cause and eliminate

Defective solenoid

Replace

Cause

Remedy

Blower Fan protection relay and fuses

Check and replace if required

Air pressure switch not changed over or defective

Check and replace if required

Defective Blower Fan

Replace Blower Fan

Defective power contactor

Replace contactor

Blower Fan starts but stops after 20-25 secs

Check for solenoid leaks

Blower Fan starts, but stops after about 10 secs in preventilating mode

Air pressure switch fails to change over; replace switch if defective; clean switch if dirt has accumulated; check electrical connections