Normal - No Call for Heat
Probable Causes
Diagnostic Steps
- No action needed - furnace is in standby
Lockout Retry / Recycle
Probable Causes
- Ignition failure
- Flame loss during run
Diagnostic Steps
- Check gas supply
- Clean flame sensor
- Test igniter
Normal - Call for Heat Active
Probable Causes
Diagnostic Steps
- No action needed - furnace is heating
Pressure Switch Open
Probable Causes
- Blocked vent
- Inducer issue
- Hose fault
Diagnostic Steps
- Inspect flue
- Check hose
- Test inducer motor
Limit / Rollout Switch Open
Probable Causes
- Dirty filter
- Airflow restricted
- Rollout trip
Diagnostic Steps
- Replace filter FIRST
- Check rollout switches
- Inspect heat exchanger if rollout
Open Fuse / Loss of Flame
Probable Causes
- Blown 3A fuse on board
- Short in low voltage circuit
Diagnostic Steps
- Check board fuse
- Inspect low voltage wiring for shorts
- Check thermostat connections
Flame Without Gas Valve Call
Probable Causes
- Leaking gas valve
- Board malfunction
Diagnostic Steps
- STOP - potential safety hazard
- Turn off gas
- Replace gas valve