Unit shuts down during long hot water use and displays Code 16 (over-temperature warning)

Safety first: Turn OFF power and gas. Hot water scalding risk is present; keep outlet temperature at or below manufacturer recommendations (often 120°F/49°C for residential).

Steps to check:

• Check water flow: Ensure all isolation valves are fully open. Clean the cold water inlet filter screen.
• Reduce temperature setting: Lower the set temperature on the controller and test again.
• Consider descaling: If the unit is older or in a hard water area, schedule a professional descaling of the heat exchanger.
• Reset and test: After adjustments, restore power and gas, reset the unit, and run hot water while monitoring temperature.

When to call a professional: If Code 16 persists, the outlet thermistor or control board may be faulty, or severe scale may be present. A technician should diagnose and correct the issue.