Water heater makes a high-pitched whistling or hissing noise when running

Safety first: Use caution around hot pipes and fittings.

Steps:

• 1. Adjust valves: Ensure inlet and outlet valves are fully open. Slightly closing a valve downstream may reduce noise in some cases.
• 2. Clean restrictors: Remove and clean any flow restrictors or filters at the heater inlet or outlet.
• 3. Check pressure: Measure inlet water pressure. If above manufacturer limits, install or adjust a pressure-reducing valve.
• 4. Descale: Perform a descaling procedure if scale buildup is suspected.

Note: Persistent loud noise may indicate internal damage and should be evaluated by a technician.