Noritz NR98 & NR111 Code 10
Combustion fault, BTU drop. Noritz labels this combustion abnormality with a BTU drop and notes that the unit continues working. The heater has seen its own output fall short and kept running rather than stopping. The checks are abnormal combustion and the flue for blockage or obstruction, and the power has to be cycled to clear it. Noritz gives this range 90 and 99 for combustion faults that stop the unit and 10 for the one that does not, with no intermediate grades. The NRC661 and NRC711 table spreads the same ground across 901, 902, 903 and 908 — more numbers, and more to go on when something is intermittent.
Also displayed as: F10
Call a proThe verdict
Call a licensed plumber
Worth acting on precisely because the unit did not stop. A heater quietly under-firing is short of air or short of gas, and the vent terminal outside is the free thing to rule out first.
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 NR98 & NR111 — not averaged across the brand.
Source: Noritz Service Manual — NR50 / NR66 / NR71 / NR98 / NCC199 / NRC111 / NR111 / NC380 (Rev. July 2011) (p. 56), 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
The same code number can mean something different on another series — make sure you're reading the page for your exact unit: