16
Noritz Tankless Water Heater
Severity: CriticalWhat it means
Noritz code 16 means the outgoing water temperature climbed higher than the safety limit — the unit shut the burner so you don't get scalded.
The usual causes are a hot-water-outlet thermistor reading wrong, scale buildup throwing off heat transfer, or a recirculation loop returning water that's already hot so the unit overshoots.
It can also be a stuck water-flow servo inside the unit.
Until it's resolved, expect the burner to keep cutting out.
Affected Models
- Noritz NRC66, NRC83, NRC98, NRC111
- Noritz NRCP series (with built-in recirculation pump)
- Noritz EZ98, EZ111
- Noritz NR66, NR83, NR98
- Noritz GQ-C series
Common Causes
- Hot-water-outlet thermistor reading inaccurately (often from scale on the probe)
- Limescale in the heat exchanger upsetting how the unit modulates
- Recirculation loop returning hot water, so the unit overshoots the setpoint
- Water-flow servo (the valve that meters flow through the unit) sticking
- Set temperature very high combined with a low draw
- Air trapped in the heat exchanger after maintenance
How to Fix It
-
Cool down and reset.
Power off at the panel, wait 10-15 minutes, power back on, run a hot tap at moderate flow.
If code 16 returns fast, something's genuinely off — keep going.
If it clears, still work through the steps below; it tends to come back. -
Lower the set temperature a notch.
On the remote controller, drop the setpoint a few degrees as a test.
If code 16 stops, the unit was overshooting at the high setting — fine as a workaround, but a thermistor or scale is the underlying reason it can't hold the higher temperature accurately. -
Check the recirculation setup.
If you have a recirc pump or a crossover valve under a far sink, the unit can see warm water arriving and overheat trying to add to it.
Confirm the recirc mode is configured correctly for your plumbing, and that the pump runs on a sensible schedule rather than constantly. -
Descale the heat exchanger and thermistor.
Circulate white vinegar or a commercial descaler through the service valves for 45-60 minutes, then flush clean.
Scale on the heat exchanger and the outlet thermistor is a very common reason a Noritz starts overshooting and tripping code 16. -
If it persists, the thermistor or flow servo needs replacing.
Setpoint lowered, recirc sane, unit descaled — and code 16 still trips? Then the outlet thermistor or the water-flow servo is the failed part.
That's a Noritz service-tech diagnosis and replacement.