Rinnai RH180 Hybrid Code 72
Flame sensing device fault. The flame rod circuit is reporting a fault. Rinnai's list for the RH180 is the longest of any sensor code in this table: verify the flame rod is touching the flame when the unit fires, check all wiring to the flame rod, remove the rod and check it for carbon build-up and clean it with sandpaper, check inside the burner chamber for foreign material blocking the flame at the rod, measure the micro amp output of the sensor circuit with flame present, and replace the rod.
Call a proThe verdict
Call a licensed plumber
The part is one of the cheapest in the appliance and carbon build-up is the usual cause, which makes this a comparatively cheap service call. It is still a service call: every step requires the burner chamber open, and one of them requires a live flame.
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 lights and then shuts down, or never lights, and tell the technician.
- Call a licensed professional. Cleaning a flame rod means opening the burner chamber, and measuring its output means doing it with the burner lit.
Frequently asked questions
How is 72 different from code 12?
Code 12 is the unit not seeing a flame it expects. Code 72 is the flame sensing circuit itself reporting a fault. They share the flame rod as a suspect, and Rinnai's checks overlap, but 72 points at the detection hardware rather than at the combustion.
Code 72 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
One other Rinnai RH180 Hybrid code points at flame detection 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: