Water heater makes loud banging or knocking noises when the burner starts or stops.

Safety: Loud bangs can indicate stress on pipes or the tank. Inspect the system promptly.

• 1. Secure pipework: Check that hot and cold pipes near the ACV heater are properly clipped and supported. Add pipe clips where needed.
• 2. Install water hammer arrestors: If bangs occur when taps or solenoid valves close, fit water hammer arrestors on the affected lines.
• 3. Reduce temperature rise: Lower the burner rate (if adjustable) or DHW setpoint slightly to reduce expansion stress.
• 4. Descale heat exchanger: Kettling (boiling sounds) often indicates scale. Arrange for descaling of the ACV heat exchanger.

Persistent or worsening noises should be evaluated by a professional to rule out structural issues.