Boiler shows “Err 13” and shuts down, often after running at high fire

Safety first: Turn off power and gas. High flue temperatures can damage components and create safety hazards.

• Inspect flue sensor: Locate the flue gas temperature sensor on the exhaust outlet. Check that it is firmly attached and its wiring is intact.
• Check venting: Ensure vent pipes are properly sized and installed per Burnham instructions. Look for sags, long unsupported runs, or signs of overheating.
• Visual heat exchanger check: Remove burner access and inspect the heat exchanger for heavy soot or scale. A dirty exchanger raises flue temperature and must be cleaned professionally.
• Reset and test: After basic checks, restore power and gas, reset the control, and observe operation. If Err 13 recurs, a technician should verify combustion, gas input, and may replace the flue sensor.