Lockout due to Ignition Failure
Probable Causes
- No gas supply
- Bad igniter
- Dirty flame sensor
- Gas valve fault
Diagnostic Steps
- Check gas supply is on
- Test igniter resistance
- Clean flame sensor
- Test gas valve
Low Heat
Probable Causes
- Normal first stage operation
Diagnostic Steps
- No action needed
Pressure Switch Stuck Open
Probable Causes
- Blocked vent
- Bad hose
- Inducer failure
- Drain blocked
Diagnostic Steps
- Check vent termination
- Inspect switch hose
- Test inducer
- Clear drain
High Heat
Probable Causes
- Normal second stage operation
Diagnostic Steps
- No action needed
Pressure Switch Stuck Closed
Probable Causes
- Failed pressure switch
- Inducer won't stop
Diagnostic Steps
- Test pressure switch
- Check inducer relay on board
Pressure Switch Open
Probable Causes
- Blocked flue
- Bad inducer
- Cracked heat exchanger
Diagnostic Steps
- Check flue
- Verify inducer
- Inspect pressure switch
Open Limit Switch
Probable Causes
Diagnostic Steps
- Replace filter
- Check returns
- Test blower motor
Limit Circuit Open
Probable Causes
- Dirty filter
- Bad blower
- Blocked duct
Diagnostic Steps
- Replace filter
- Check blower
- Check ductwork
Flame Sensed Without Call for Heat
Probable Causes
- Leaking gas valve
- Board short
Diagnostic Steps
- STOP - gas safety concern
- Close gas manually
- Test gas valve
Flame Sensed Out of Sequence
Probable Causes
- Flame sensor issue
- Gas valve stuck open
- Board failure
Diagnostic Steps
- Replace flame sensor
- Test gas valve
- Check board
Line Voltage Polarity Reversed
Probable Causes
- Hot/neutral reversed at outlet
Diagnostic Steps
- Check outlet wiring
- Correct polarity
Ignition Lockout
Probable Causes
- Bad igniter
- No gas
- Flame sensor dirty
Diagnostic Steps
- Check igniter
- Verify gas supply
- Clean flame sensor
Gas Valve Circuit Failure
Probable Causes
- Bad gas valve coil
- Board gas output fault
- Wiring damage
Diagnostic Steps
- Test gas valve coil resistance
- Check board output
- Inspect wiring
Rollout Switch Open
Probable Causes
- Flame rollout condition
- Heat exchanger crack
- Blocked heat exchanger
Diagnostic Steps
- DO NOT BYPASS
- Inspect heat exchanger
- Check burners