Water heater locks out with E02, and the burner stops shortly after an ignition attempt.

Safety: Turn off electrical power before opening any covers. If the flame extinguishes repeatedly, do not continuously reset the unit; thoroughly investigate the underlying cause.

• 1. Visual flame check: Through the sight glass (if fitted), observe the flame when the unit is operating. A stable flame should be blue and even. Yellow, lifting, or pulsing flames typically indicate combustion issues.
• 2. Inspect ionization electrode: Remove the burner cover. Clean the ionization rod with a fine abrasive pad, ensuring there is no carbon buildup. Confirm the correct gap and position as per the ACV service manual, and ensure that the cable is not damaged or touching any metal parts.
• 3. Check burner surface: Remove the ACV premix burner and inspect it for corrosion, blocked ports, or debris. Clean gently with a soft brush and vacuum. Reinstall with correct gasket alignment.
• 4. Verify condensate drain: On condensing ACV water heaters, a blocked condensate trap can flood the combustion chamber and disturb the flame. Check the ACV condensate trap and its drain hose for any blockage and clean/flush as needed.
• 5. Gas supply stability: If other gas appliances in the property show issues, or if the flame drops when other gas loads start, have a qualified gas technician check the supply pressure and regulator operation.

If the E02 error continues, the burner control board or gas valve may be defective and should be tested and replaced by an ACV-authorized technician.