Furnace causes banging or knocking noises in the pipework when starting or stopping.

Safety first: Turn off power before adjusting pump settings.

• Bleed air: Bleed radiators and high points to remove trapped air that can cause banging.
• Adjust pump speed: If the Sime pump has multiple speeds, try a lower setting to reduce water hammer.
• Secure pipework: Add or tighten pipe clips where pipes move or knock against walls or joists.
• Check zone valves: Slow‑acting valves reduce hammer; consult a technician if existing valves close too abruptly.