What does 79 mean?
Ignition sequence completed but no gas or flame detected at burners.
Common causes
- Gas supply shut off
- Failed gas valve
- Low gas pressure
- Failed hot surface igniter
- Incorrect gas type - LP vs NG mismatch
Diagnostic & testing steps
- 1. Verify gas supply valve is fully open
- 2. Check gas pressure at inlet: 5-7 in WC (NG), 10-11 in WC (LP)
- 3. Test gas valve coil resistance: 40-80 ohms
- 4. Verify 24VAC at gas valve terminals during call for heat
- 5. Test igniter resistance: 40-200 ohms (failed if open)
Tools required
- Multimeter
- Manometer
- Gas pressure gauge
OEM parts & part numbers
Gas Valve, Hot Surface Igniter
Part numbers: MOD00963, IGN00113
Safety warning
⚠️ GAS HAZARD: Never bypass gas valve safety controls. Check for gas odor before proceeding.
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