Noritz NCC199 & NRC111 Code 90
Combustion fault. Combustion abnormality, in two grades. Noritz prints the warning indication and the shutdown under the same number: the warning checks abnormal combustion and the flue for blockage, and the shutdown adds checking that the flame ignites all the way across the burner and requires a power cycle to clear.
Also displayed as: F90
Call a proThe verdict
Call a licensed plumber
Check the vent terminal outside, because it is free and it is a common cause. Everything past it is combustion, and a unit reporting abnormal combustion indoors is one to leave off rather than keep restarting.
Typical cost: $0–$1,000
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 NCC199 & NRC111 — not averaged across the brand.
Source: Noritz Service Manual — NR50 / NR66 / NR71 / NR98 / NCC199 / NRC111 / NR111 / NC380 (Rev. July 2011) (p. 55), 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.
- Go outside and check the vent terminal and air inlet for snow, leaves, a nest, or anything built against them.
- Do not take any vent section apart yourself.
- Call a licensed professional.
Code 90 on other Noritz series
Noritz keeps the same fault name for code 90 on some series and not others. Check the one that matches your rating label:
Don't confuse this with
2 other Noritz NCC199 & NRC111 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: