10
Noritz Tankless Water Heater
Severity: ModerateWhat it means
Noritz code 10 means the unit failed its airflow check — air supply or exhaust is restricted, so it won't fire the burner.
Nine times out of ten the cause is at the vent terminal outside: a bird nest, leaves, lint from a nearby dryer vent, or snow and ice over the screen.
It also shows up when the vent run is longer or has more elbows than the model allows, or when the combustion fan is slowing down.
Until the air path checks out you get no hot water.
Affected Models
- Noritz NRC66, NRC83, NRC98, NRC111 (residential condensing)
- Noritz NRCP series (with built-in recirculation pump)
- Noritz EZ98, EZ111 (tankless replacement series)
- Noritz NR50, NR66, NR83, NR98 (older non-condensing)
- Noritz GQ-C series condensing units
Common Causes
- Vent or intake terminal blocked — nest, leaves, lint, snow, ice
- Vent run longer or with more elbows than the model's published limit
- Intake and exhaust terminals mounted too close together (exhaust gets re-drawn)
- Sagging vent pipe holding a slug of condensate
- Combustion fan slowed by dust on the wheel or a worn bearing
- Wrong vent diameter or unapproved vent material
How to Fix It
-
Walk outside to the vent terminal.
This clears the majority of code 10s.
Find the intake and exhaust pipes where they exit the wall or roof.
Pull out any nest, leaves, or lint, and brush snow or ice off the screens.
If a dryer or kitchen exhaust nearby is dumping lint onto them, that's worth sorting too. -
Reset and test.
Press the power button off, wait ten seconds, power back on, run a hot tap.
If you cleared a blockage, code 10 should be gone.
If it comes back with the terminals clearly open, the vent design or the fan is the issue. -
Check the inlet air filter (if your model has one).
Turn off the unit's breaker, open the cover, and look for the air intake screen or filter.
Months of dust restrict airflow.
Vacuum it gently or wipe with a soft cloth, then close up. -
Confirm the vent length is within spec.
Noritz publishes a maximum equivalent vent length per model, and every elbow counts as several feet.
If the install is over the limit — or the intake and exhaust caps sit closer together than the manual allows — code 10 keeps returning.
The fix is to shorten the run, upsize the pipe, or move a terminal. -
Check the combustion fan.
Breaker off — flick the fan wheel near the top of the unit.
It should spin freely and quietly.
A dust-caked wheel: vacuum it.
A grinding bearing: the fan motor needs replacing, which is usually a service-tech job. -
Still failing? Get the fan or pressure sensor checked.
Terminals clear, vent within spec, no sags, fan spins clean — then the combustion fan is underperforming or the air-pressure sensor on the board is bad.
That's a Noritz service call to test and replace.
Frequently Asked Questions
Why does code 10 keep showing up every winter?
Frost and snow at the vent terminal.
A condensing tankless puts out a visible plume of moist exhaust, and in cold weather that builds frost on the screen and around the cap — worst on low sidewall terminals near the ground.
Brushing it clear gets you running again; raising the terminal or fitting a manufacturer-approved cold-climate vent kit stops it recurring.