Rinnai RH180 Hybrid Code 73
Burner sensor circuit fault. The circuit between the burner sensor and the board is faulty, as distinct from the sensor being out of range. Rinnai's remedy on the RH180 is two lines: check the sensor wiring and the PCB for damage, and replace the sensor.
Call a proThe verdict
Call a licensed plumber
Rinnai names the PC board as well as the sensor here, which is what makes the range wide: a chafed harness at the burner is cheap, a damaged board is not. Both are inside the cabinet on the burner side.
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 RH180 Hybrid — not averaged across the brand.
Source: Rinnai RH180 Operation and Installation Manual (100000319) (p. 36), 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.
- Note whether the code is constant or comes and goes with the unit firing — an intermittent fault points at the harness rather than the board.
- Call a licensed professional. Rinnai's own checks here are the wiring at the burner and the PC board.
Frequently asked questions
What is the difference between code 31 and code 73?
Rinnai splits the burner sensor into two codes on this appliance. Code 31 is the sensor itself — the remedy is simply "replace sensor". Code 73 is the circuit around it, and Rinnai adds the PC board to the list of things to inspect.
Code 73 on other Rinnai 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
5 other Rinnai RH180 Hybrid codes point at a sensor 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: