Boiler makes loud banging or knocking noises when starting or stopping

Safety first: Turn off power before bleeding air or adjusting valves. Hot water can scald.

• 1. Bleed air: Use air vents on radiators and high points to remove trapped air. Air can cause banging and gurgling.
• 2. Check flow: Ensure all zone valves are open when calling for heat and that circulators are running. Low flow through the heat exchanger can cause kettling (tea-kettle-like noises).
• 3. Inspect piping supports: Look for loose or unsupported pipes that move when the boiler starts or stops. Add or tighten pipe hangers.
• 4. Descale if needed: Persistent kettling often indicates scale inside the heat exchanger. This requires professional chemical cleaning or flushing.