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