Boiler or nearby piping makes loud banging or knocking noises when starting or stopping.

Safety: No immediate hazard in most cases, but loud banging should be addressed to prevent damage.

• 1. Bleed air: Remove air from radiators and high points to reduce sudden flow changes.
• 2. Check expansion tank: Ensure the hydronic expansion tank is present, properly sized, and not waterlogged (tap it; it should sound hollow at the top).
• 3. Secure piping: Inspect accessible piping near the Noritz boiler and add or tighten pipe clamps and supports where movement occurs.
• 4. Water hammer arrestors: If banging occurs when valves close, have a plumber install water hammer arrestors or adjust valve closing speed.