A.O. Smith water heater makes a high-pitched whistling or screeching noise when running

Safety: Use caution when working on hot water lines; allow to cool if necessary.

• 1. Check valves: Ensure the cold water shutoff valve to the heater is fully open.
• 2. Inspect inlet screen: On tankless or hybrid models, clean the cold water inlet filter screen.
• 3. Heat trap nipples: If installed, remove and inspect heat trap nipples for debris or scale. Replace if noisy or restricted.
• 4. Mixing valve: If a thermostatic mixing valve is installed, clean or replace its internal cartridge.