Rinnai RH180 Hybrid Code 31
Burner sensor fault. The burner sensor is out of range or not reporting. Rinnai's remedy on the RH180 is a single line — replace the sensor — with none of the wiring and resistance checks it gives for the other sensor codes on this appliance.
Call a proThe verdict
Call a licensed plumber
An inexpensive part, but it sits at the burner, which is the one place on a gas appliance a homeowner has no business opening. Rinnai gives no intermediate check here: the answer is a new sensor, fitted by someone qualified.
Typical cost: $150–$600
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 unit still fires at all and tell the technician.
- Call a licensed professional. The sensor is at the burner and Rinnai's remedy goes straight to replacement.
Frequently asked questions
Rinnai's other document lists code 31 for both the RH180 and the Non-SENSEI series. Which page do I read?
This one, if you own an RH180. Code 31 appearing as a separate bullet from "Non-SENSEI Series" in document 100000652 is one of the inconsistencies that made the RH180 impossible to build from that document. The RH180's own manual states it directly, and that is what this page uses.
Code 31 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: