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
The same code number can mean something different on another series — make sure you're reading the page for your exact unit: