Boiler makes loud banging or knocking noises (kettling) during operation

Safety first: Turn off power and allow the boiler to cool before touching any pipes or components.

• Step 1 – Check system flow: Ensure all isolation valves are fully open and that zone valves are operating correctly. Clean any system strainers or filters.
• Step 2 – Assess water quality: Bleed a small amount of water from a radiator or drain. Dark, sludgy water indicates contamination that can cause kettling.
• Step 3 – Chemical treatment: Add an appropriate hydronic system cleaner and run the system per manufacturer instructions, then flush and refill with inhibitor. This is best done by a heating professional.
• Step 4 – Descale heat exchanger: In hard water areas, the primary heat exchanger may need to be chemically descaled using a pump and approved descaling solution. This should be performed by a qualified technician familiar with Rheem boilers.
• Step 5 – Monitor operation: After cleaning, noises should be significantly reduced. Persistent kettling may require heat exchanger replacement.

Warning: Ignoring kettling can lead to localized overheating and premature heat exchanger failure.