Rinnai error code 38
It depends on your series. Code 38 does not point at the same fault on every Rinnai unit. Find your series in the table below before you buy a part or book anyone.
What code 38 means on each Rinnai series
| Series | What it means | Verdict | Typical cost |
|---|---|---|---|
| Non-SENSEI | Exhaust gas temperature sensor fault | Call a pro | $150–$600 |
| RH180 Hybrid | Carbon monoxide or flammable vapour sensor fault | Call a pro | $150–$700 |
| SENSEI | Exhaust gas temperature sensor fault | Call a pro | $150–$600 |
| SENSEI RX | Exhaust gas temperature sensor fault | Call a pro | $150–$600 |
Each series links to the full page: what the manufacturer's manual says for that generation, what you can safely check yourself, and what the repair should cost.
How much the answer changes between series
Every Rinnai series that documents code 38 routes it the same way: a professional. That is unusual enough to be worth saying, because on this brand the same number often means different work on different generations. Here it does not — so you can act on this page without first establishing which unit you own.
The spread is real money. On the Non-SENSEI the worst case is $600; on the RH180 Hybrid the same number can reach $700. Identify your series before you agree to anything.
Which Rinnai do you have?
The model number is on the rating label on the unit itself. Match it against the list below — or use the full model-number decoder.
Where this comes from
Source: Rinnai Troubleshooting Tankless Water Heater Diagnostic Codes (100000652) (p. 42), read Aug 2026 — the manufacturer's own documentation for this Rinnai range.
Source: Rinnai RH180 Operation and Installation Manual (100000319) (p. 36), read Sep 2026 — the manufacturer's own documentation for this Rinnai range.
Parts, guides and symptoms behind code 38
Everything the 4 Rinnai series point at for this code, in one list. A part named here is one the manufacturer's own procedure reaches for.