Boiler displays error 16 and shuts down after running for a short period, often at high demand.

Safety first: Turn off power and allow the boiler to cool. Hot water circuits may be under pressure and at high temperature.

• Verify all valves are open: Confirm that the boiler's cold inlet, heating flow, and return valves are fully open. Check any zone valves for proper operation.
• Clean inlet water filter: Many Rinnai boilers have a mesh filter on the cold water inlet. Isolate the water, remove the filter, rinse debris, and reinstall.
• Check system pressure: For sealed systems, ensure the pressure gauge is within the recommended range (typically 1.0–1.5 bar when cold). Repressurize if needed following the manual.
• Descale plate heat exchanger: If domestic hot water temperature spikes quickly, the DHW plate heat exchanger may be scaled. A professional should chemically flush or replace the plate exchanger.
• Reset and test: Restore power and water, reset the boiler, and monitor outlet temperature. If error 16 recurs, the outlet thermistor or control board may require replacement.