Water heater emits a high-pitched whistling or humming noise during operation.

Safety: Noise alone is not usually dangerous but can indicate restrictions.

• Check valves: Ensure cold inlet and hot outlet service valves are fully open.
• Adjust flow: Slightly reduce flow at the tap to see if the noise changes or disappears.
• Secure panels: Tighten screws on the front cover and side panels to reduce vibration.
• Service burner: If whistling persists, have the burner and injectors cleaned by a technician.