Water heater emits a whistling or high-pitched noise when hot water is running.

Safety: Turn off water supply before removing filters or fittings.

Steps:

• Clean inlet filter: Remove and clean the cold water inlet mesh filter.
• Check valves: Ensure all service valves are fully open; a half-open valve can cause whistling.
• Inspect flow restrictor: Some Sime models have a flow restrictor in the inlet. Remove and clean it if accessible.

Professional help: If noise persists, a technician should inspect the hydraulic group and internal waterways for scale or damage.