Furnace shows A02 and shuts down shortly after ignition attempt, flame appears but goes out quickly

Safety: Disconnect power and close the gas valve before removing covers. Allow the furnace to cool.

• Visual flame check: After re-energizing (with panels in place), observe through the sight glass during startup. A weak, yellow, or lifting flame suggests gas or burner issues.
• Clean burner and flame sensor: With power and gas off, remove the burner cover. Clean burner ports with a soft brush and compressed air (low pressure). Remove the ionization probe and clean it with a fine abrasive pad. Reinstall securely.
• Check condensate drain (for condensing Beretta models): A blocked condensate trap or hose can disturb combustion. Inspect the condensate trap and hoses for sludge or kinks. Flush the trap with clean water and reassemble, ensuring all seals are tight.
• Inspect grounding: Ensure the furnace chassis is properly grounded and that the ground wire to the control board is tight. Poor grounding can cause flame detection issues.

If A02 persists after cleaning and basic checks, a technician should measure gas pressure and verify gas valve and control board operation.