Boiler display shows “Err 5” and burner shuts down after ignition, often within a few seconds

Safety first: Turn off power and gas before removing burner components. If you smell gas, do not attempt repairs yourself.

• Observe flame (if possible): Through the sight glass, watch the burner when it lights. A proper flame should be stable, mostly blue with minimal yellow tips. Flame that lifts off, pulses, or goes out indicates supply or burner issues.
• Clean flame sensor: Remove the flame rod and gently clean it with fine abrasive pad. Oil or oxidation reduces the flame signal. Reinstall and ensure the ceramic insulator is intact.
• Inspect burner: Remove the burner assembly following the Burnham manual. Vacuum dust and lint, and brush off any rust or scale from the burner head and ports. Do not enlarge burner holes.
• Check gas shutoff and flex connector: Confirm the manual gas valve is fully open and the flexible connector is not kinked. Other gas appliances should operate normally; if not, contact the gas utility.
• Reset and test: Restore gas and power, reset the control, and call for heat. If the flame still drops out and Err 5 returns, a technician should measure gas pressure and flame rectification microamps and may need to replace the gas valve.