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