No Previous Error
Probable Causes
- Normal operation
- No fault stored
Diagnostic Steps
- System is operating normally
- No action needed
High Pressure Alert
Probable Causes
- Dirty condenser
- Restriction
- Overcharge
- Non-condensables
Diagnostic Steps
- Clean condenser
- Check charge
- Verify fan operation
Low Pressure Alert
Probable Causes
- Low charge
- Frozen evaporator
- Restriction
Diagnostic Steps
- Check charge
- Check filter
- Check TXV
Compressor Thermal Overload
Probable Causes
- High head pressure
- Low charge
- Bad capacitor
Diagnostic Steps
- Check pressures
- Test capacitor
- Verify airflow
System Lockout - Retries Exhausted
Probable Causes
- Repeated ignition failure
- Gas supply issue
- Flame sensor fault
Diagnostic Steps
- Power cycle to reset
- Check gas supply
- Clean flame sensor
- Test igniter
Pressure Switch Error
Probable Causes
- Blocked vent
- Bad pressure switch
- Inducer failure
- Hose disconnected
Diagnostic Steps
- Check flue and intake pipes
- Inspect hose connections
- Test pressure switch
- Test inducer motor
Open High Limit
Probable Causes
- Dirty filter
- Blocked return
- Slow blower
- Oversized unit
Diagnostic Steps
- Replace filter
- Check all returns open
- Test blower speed
- Check gas pressure
Flame Sensed Without Gas Valve Call
Probable Causes
- Gas valve leaking through
- Short in flame circuit
- Board fault
Diagnostic Steps
- STOP - potential gas leak
- Close manual gas valve
- Test gas valve
- Replace board if needed
Power or Low Voltage Interrupt
Probable Causes
- Power flicker
- Thermostat wire issue
- Transformer weak
Diagnostic Steps
- Check voltage at transformer
- Inspect thermostat wiring
- Test for loose connections
Gas Valve Circuit Error
Probable Causes
- Bad gas valve
- Wiring to gas valve
- Board output failure
Diagnostic Steps
- Test gas valve coil resistance
- Check wiring to gas valve
- Test board gas valve output
Low Discharge Temperature
Probable Causes
- Low refrigerant charge
- Compressor failure
- Lost charge
Diagnostic Steps
- Check charge
- Look for leaks
- Test compressor
Discharge Temperature Too High
Probable Causes
- Dirty condenser
- Restriction
- Non-condensables
Diagnostic Steps
- Clean condenser
- Check charge
- Recover and recharge
Check Polarity / Ground Fault
Probable Causes
- Hot and neutral reversed
- No ground wire
- Floating neutral
Diagnostic Steps
- Check outlet polarity with meter
- Verify ground connection
- Check panel wiring
Low Evaporator Temp
Probable Causes
- Low airflow
- Dirty filter
- Low charge
Diagnostic Steps
- Check filter
- Check ductwork
- Check charge