Heater makes loud banging or knocking noises during operation, especially at startup.

Safety First: Turn off power and gas. Allow the heater to cool before touching plumbing or internal parts.

• Check flow and filter: Ensure the pump is running at adequate speed and the filter is clean. Low flow can cause water to flash to steam inside the exchanger.
• Bleed air: If your system has air bleeders near the heater, open them to release trapped air.
• Inspect for scale: Persistent banging often indicates scale. A professional should inspect and, if necessary, chemically descale or replace the heat exchanger.
• Review plumbing: Avoid sudden valve closures or pump speed changes that can cause water hammer.