Noritz error code 10: combustion abnormality warning

Code 10 tells you the heater is not burning as cleanly as it should. It may still make hot water for now, but Noritz treats it as a warning of a more serious shutdown.

The meaning below comes from Noritz's own technical knowledge base. Noritz technical support: 866-766-7489.

What causes it

• Installation settings that do not match the home: elevation, vent type, vent length, vent size and common venting.
• Low air flow from incorrect venting or dirty, clogged vent terminations or filters.
• Low gas flow from an undersized gas line, a long gas run or a gas meter that is too small.

On newer Pro series models, installers can check and change settings with the buttons on the circuit board or the Noritz EZ Start Plus app.

What you can check

1. Clear any leaves, snow or nests from the intake and exhaust terminals outside.
2. Note whether code 10 shows up when other gas appliances run at the same time.
3. If the heater was recently installed or moved, ask the installer to confirm the setup settings.

Noritz notes that some models record code 10 only in the error history, where it is a technician's reference rather than an active fault.

How to reset it

Turn the heater off at the remote controller and back on. If the code stays, disconnect the unit's electrical power for about 30 seconds, then restore it. If the code comes straight back, the cause is still there.

Before you call

Have the model and serial number from the rating label ready, along with the exact code and when it appears: at startup, during use, or only at high demand. Mention any recent work on the gas, water or electrical supply and when the heater was last serviced. This helps the technician bring the right parts and often saves a second visit.

See every code on our Noritz error codes page.