Noritz NRC Series Code 90
Air flow or combustion fault. The unit has shut off over air flow or combustion. Noritz's base check is the flue and air inlet for blockage or obstruction, and the display window separates the severity: 901 is a warning that escalates to a shutdown, 902 adds checks of whether the flame ignites all across the burner and of the gas solenoid valves, 903 is another shutdown, and 908 is the unit locked out, which Noritz says requires contacting the nearest Noritz agent rather than a power cycle.
Also displayed as: 901, 902, 903, 908
Call a proThe verdict
Call a licensed plumber
Check the vent terminal outside, because that is free and it is genuinely a common cause. Everything past it is combustion, and a unit reporting abnormal combustion in a house is the one case where leaving it off costs less than a cold shower.
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 NRC Series — not averaged across the brand.
Source: Noritz Service Manual — NR501-OD, NR662-OD, NRC661, NRC711 (Rev. Dec 2013) (p. 28), 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.
- Note the three-digit code from the display window — 908 means the unit has locked out and Noritz requires an agent to clear it.
- Do not take any vent section apart yourself.
- Call a licensed professional.
Frequently asked questions
My display shows 908 and cycling the power does nothing. Is it broken?
It is locked, not broken. Noritz's remark against 908 is to contact the nearest Noritz agent — unlike the other 90x codes, this one is not cleared by disconnecting power. The unit has seen the fault enough times to stop offering you a retry.
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: