Noritz NR50, NR66 & NR71 Code 90
Combustion fault. Combustion abnormality, in two grades under one number. The warning indication checks abnormal combustion and the flue for blockage; the shutdown adds checking that the flame ignites all the way across the burner and needs a power cycle to clear. Continuous flashing on a unit with no remote controller.
Also displayed as: continuous flashing
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 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.
- 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: