Heater starts, flame appears briefly, then shuts down and displays E03.

Safety first: Switch off power and gas before opening the heater. Flame instability can cause delayed ignition or small explosions; do not repeatedly reset without inspection.

• Check gas supply stability: Ensure the gas shutoff is fully open and that there are no other large gas loads cycling on/off at the same time. If you smell gas, stop and call a professional immediately.
• Inspect burner and combustion area: Remove the front panel and burner cover. Look for rust, scale, or debris on the Kripsol burner tray. Clean with a soft brush and vacuum. Make sure all burner ports are clear.
• Verify ground connection: Confirm that the heater’s ground wire is securely attached to the chassis and that the supply ground is intact. Poor grounding can cause the flame sensor to misread.
• Check flame sensor wiring: Inspect the wire from the flame sensor to the Kripsol control board for damage or loose connectors. Reseat connectors firmly.
• Restart and observe: Restore power and gas, then start the heater while observing through the sight glass. If the flame lights and then drops out repeatedly, the control board or gas valve may need replacement by a technician.