Furnace makes loud banging or knocking noises when starting or stopping.

Safety: Sudden noises can indicate stress on the system; inspect promptly.

• Secure pipework: Check visible pipes near the furnace and secure any that move when the furnace starts or stops.
• Bleed air: Remove air from radiators and high points to reduce sudden flow changes.
• Check pump speed: If the pump has adjustable speed, try a lower setting to reduce flow velocity (refer to Ariston manual).
• Thermostatic radiator valves: Avoid having all TRVs nearly closed; keep at least one radiator fully open to act as a bypass.