Rinnai RH180 Hybrid Code 35
Tank temperature sensor fault. The sensor reading the storage tank temperature is out of range. This code exists nowhere else in the Rinnai range for the simple reason that no other Rinnai water heater on this site has a tank. Rinnai's list is wiring, resistance, and one item specific to the layout — verify the sensor is properly positioned on the tank surface — before replacing it.
Call a proThe verdict
Call a licensed plumber
Inexpensive, and one of Rinnai's four steps is that the sensor may simply have come off the tank surface rather than failed. Still a service call: it is inside the cabinet of a gas appliance, and a misread tank temperature is what decides when the burner fires.
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 what the unit is doing wrong as well as the code — short cycling, lukewarm water, or nothing at all — and tell the technician.
- Call a licensed professional. Rinnai's first check is whether the sensor is still seated on the tank, which is a quick find if you mention it.
Frequently asked questions
Why does no other Rinnai have a code 35 like this?
Because no other Rinnai on this site stores water. The RH180 is a hybrid — a tankless engine on a storage tank — so it needs a sensor for the tank, and a fault code for that sensor. A tankless unit heats water as it passes and has nothing to measure.
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: