Noritz NR50, NR66 & NR71 Code 10
Combustion fault, BTU drop. Combustion abnormality with a BTU drop, and Noritz notes the unit continues working. The checks are abnormal combustion and the flue for blockage or obstruction. On a unit with no remote controller this shows as continuous flashing, and Noritz records that no reset is needed — the heater is available to burn even before you reset it.
Also displayed as: continuous flashing
Call a proThe verdict
Call a licensed plumber
The appliance is under-firing and has decided to carry on. That is worth a look precisely because nothing stopped: the vent terminal outside is free to check and is the common cause.
Typical cost: $0–$900
US estimate for parts and labor. Prices vary by region and by who does the work — see how we estimate costs.
What the manual says
The meaning above is transcribed from the manufacturer's diagnostic documentation for the NR50, NR66 & NR71 — not averaged across the brand.
Source: Noritz Service Manual — NR50 / NR66 / NR71 / NR98 / NCC199 / NRC111 / NR111 / NC380 (Rev. July 2011) (p. 54), read Sep 2026 — the manufacturer's own documentation for this exact series.
What you can safely check
Before anything else: if you smell gas, stop here, leave, and call your gas utility.
- Check the vent terminal and air inlet outside for snow, leaves, a nest or anything built against them.
- Note whether hot water has been weaker than usual, and for how long.
- If the terminal is clear, call a licensed professional.
Code 10 on other Noritz series
Noritz keeps the same fault name for code 10 on some series and not others. Check the one that matches your rating label:
Don't confuse this with
2 other Noritz NR50, NR66 & NR71 codes point at combustion itself too. They are the same symptom reported from a different place in the unit, so which one the display shows is what tells you where to look: