Boiler shows error 51 and does not respond to thermostat or controller commands.

Critical safety: Do NOT attempt to disassemble or adjust the gas valve yourself. Turn OFF gas and power and contact a qualified technician if you suspect a gas valve issue.

• 1. Power cycle: Turn OFF power to the Noritz boiler for 30 seconds, then restore. Sometimes transient control errors clear with a reset.
• 2. Inspect wiring: With power OFF, remove the front cover and visually inspect the wiring harness to the gas valve. Ensure connectors are fully seated and wires are not damaged.
• 3. Check for water damage: Look for signs of leaks or condensation on the gas valve and control board. If present, the unit must be serviced and dried by a professional.
• 4. Professional service: If error 51 persists, a Noritz technician must test the gas valve coil resistance and control board outputs and replace the faulty component.