Boiler makes loud banging or kettling noises during operation, especially on heating

Safety first: Turn down the boiler flow temperature and allow the system to cool if noises are severe.

• Check system pressure: Ensure pressure is 1.0–1.5 bar cold. Low pressure can worsen kettling.
• Reduce flow temperature: Temporarily lower the CH flow temperature on the Sime control panel to reduce stress on the heat exchanger.
• Bleed radiators: Remove trapped air which can cause hot spots and noise.
• Engineer descaling: In hard water areas, an engineer may need to chemically descale or replace the primary heat exchanger and flush the system with inhibitor.
• Check pump performance: The engineer should verify that the pump is correctly sized and operating at the right speed for the system.