Rinnai Non-SENSEI Code 73
Burner thermocouple fault. A wiring or component fault at the burner thermocouple, as opposed to code 31, which is the same component reading out of range. This code exists only on the Non-SENSEI generation. Rinnai checks the harness back to the PC board and the altitude settings, confirms manifold gas pressures against factory specification for the altitude, and then replaces the thermocouple — and the PC board if the code returns.
Call a proThe verdict
Call a licensed plumber
A modest part behind a gas-side diagnosis. Rinnai's own text carries a warning that you must be qualified to service gas systems before the pressure checks, which is where this stops being homeowner work.
Typical cost: $150–$900
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 Non-SENSEI — not averaged across the brand.
Source: Rinnai Troubleshooting Tankless Water Heater Diagnostic Codes (100000652) (p. 61), read Aug 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.
- If the unit was moved, or installed at a different altitude from where it was set up, say so — altitude settings are the second item on Rinnai's list.
- Book a licensed professional.
Frequently asked questions
What is the difference between code 31 and code 73?
Both concern the burner thermocouple on a Non-SENSEI unit. Code 31 is the reading being out of range — above 30 or below 8 millivolts — which points at gas pressure or a blocked heat exchanger. Code 73 is a fault at the component or its wiring. Neither exists on the SENSEI generations.
Code 73 on other Rinnai series
Code 73 is a different fault on every other Rinnai series that documents it, which is exactly why this page is written for the Non-SENSEI alone:
Don't confuse this with
3 other Rinnai Non-SENSEI codes point at the burner 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: