Water heater makes a high‑pitched whistling or hissing noise from the piping.

Safety first: Use caution around hot pipes and fittings.

• Check valves: Ensure the cold water shutoff valve to the Giant heater is fully open.
• Inspect inlet screen: Some Giant models have an inlet filter screen. Shut off water, relieve pressure, and clean the screen if clogged.
• Mixing valve: If a thermostatic mixing valve is installed, verify it is not partially blocked. Clean or replace as needed.
• Pipe sizing: If noise occurs only at high flow, consult a plumber to verify piping is adequately sized.