Reliance water heater makes loud banging or hammering noises when water is turned on or off

Safety first: No immediate electrical or gas hazard, but repeated hammer can damage plumbing and the heater.

Steps to check:

• 1. Measure water pressure: Attach a pressure gauge to a hose bib. If static pressure exceeds 80 psi, install or adjust a pressure-reducing valve (PRV).
• 2. Install hammer arrestors: Add water hammer arrestors near quick-closing valves (dishwasher, washing machine) and, if needed, near the water heater.
• 3. Secure piping: Inspect exposed hot and cold lines near the heater. Add pipe straps or cushioning where pipes can move and bang against framing.
• 4. Check expansion tank: If an expansion tank is installed, verify it is properly charged to match system pressure. A failed tank can worsen hammer.
• 5. Adjust valve operation: Avoid slamming valves closed; close them more gradually where possible.

Note: While not a heater internal fault, addressing water hammer protects the Reliance tank and connected piping.