Noritz NRC Series Code 73
Circuit board setting fault. The board's configuration is wrong or has been changed. Noritz splits this into three display-window codes: 731 is the maintenance writers set incorrectly, 733 is the DIP switch settings — Noritz gives high elevation and vent length as the examples — and 734 is circuit board failure. The vent length and elevation settings tell the appliance how hard to run its fan, which is why this is a combustion setting and not a preference.
Also displayed as: 731, 733, 734
Call a proThe verdict
Call a licensed plumber
This code often appears right after someone has been inside the unit, or after a board replacement, because the settings did not come across. It is a professional adjustment: the switches encode elevation and vent run, and setting them wrong changes how the appliance burns gas.
Typical cost: $100–$800
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.
- Think back to whether anyone has worked on the unit recently, and tell the technician — a board swap or a vent change is the usual trigger.
- Do not open the unit to change switch positions yourself. These settings control combustion.
- Call a licensed professional.
Code 73 on other Noritz series
Other Noritz series report code 73 under the same fault name, but each manual is transcribed separately and they do not read alike:
Don't confuse this with
One other Noritz NRC Series code points at the circuit board 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: