Water temperature overshoots setpoint; unit shuts down with error code 16, often during low-flow usage such as handwashing.

Safety first: Turn OFF power and gas before servicing. Water may be very hot; open a faucet and allow water to cool before handling plumbing.

Steps to check and correct:

• Clean inlet water filter: Close cold and hot isolation valves. Remove the inlet water filter screen at the cold inlet of the Noritz unit. Rinse under running water to remove sediment. Reinstall and open valves slowly.
• Check minimum flow: Ensure the fixture aerators and showerheads are not clogged. Clean or replace them to maintain adequate flow. Noritz units require a minimum flow rate to modulate properly.
• Descale the heat exchanger: If you have hard water or see signs of scale (noise, fluctuating temps), perform a descaling flush through the service valves. This restores proper heat transfer and temperature control.
• Inspect outlet thermistor: Locate the outlet temperature sensor on the hot water outlet side. Check for secure connection and no corrosion. Replace the thermistor if wiring is damaged or readings are erratic (requires multimeter and service manual specs).
• Reset and test: Restore power and gas, then run multiple fixtures to test. If error 16 continues, have a Noritz technician evaluate the PCB and gas modulation control.