Noritz NRC Series Code 51
Gas solenoid valve failure. A gas solenoid valve, or the circuit that drives it, is not behaving. Noritz's checks are an improper connection at the valves, damage to the valve connections, and circuit board failure. The valves are what admit gas to the burner, so this is a fault in the part of the appliance that decides whether gas flows.
Also displayed as: 511
Call a proThe verdict
Call a licensed plumber
Nothing here is a homeowner check. The cheap outcome is a connector that has worked loose; the expensive one is the circuit board. Leave the unit off until it has been seen.
Typical cost: $250–$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.
- Leave the unit switched off.
- Call a licensed professional. Every item on Noritz's list for this code is inside the gas train or on the board.
Don't confuse this with
One other Noritz NRC Series code points at a valve too. They are different components in different places, and ordering a part against the wrong one is the most common way this fault gets expensive: