Control displays 'Flue Temp High' or similar; burner shuts down and may lock out until reset.

Safety first: Turn off power and gas. Hot flue surfaces can cause burns; allow time to cool. Risk of carbon monoxide exists with venting issues.

• Inspect venting: Check the flue pipe from the water heater to the termination for obstructions, disconnections, or sagging sections that can trap condensate. Clear any visible blockage and correct improper slopes.
• Check combustion air: Ensure combustion air openings or intake piping are not blocked. Inadequate air can cause hotter flue gases and poor combustion.
• Examine flue temperature sensor: Locate the flue temperature sensor on the flue outlet. Inspect wiring for damage or loose connections. If the sensor is cracked or deformed, it should be replaced.
• Do not adjust gas input yourself: Overfiring due to incorrect gas pressure or orifice size must be corrected by a qualified technician with proper instruments.
• Reset and monitor: After clearing any obvious issues, reset the control and monitor operation. If the fault recurs, schedule professional service to inspect the heat exchanger and combustion settings.