Rinnai error code 34
It depends on your series. Code 34 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 34 means on each Rinnai series
| Series | What it means | Verdict | Typical cost |
|---|---|---|---|
| Non-SENSEI | Combustion air temperature thermistor fault | Call a pro | $150–$900 |
| SENSEI RX | Lime detecting thermistor fault | Part replacement | $150–$450 |
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
This is the part that catches people out. Code 34 does not lead to the same job on every Rinnai series: a professional and a replacement part are both documented answers to this number, depending on the generation. Buying a part because a page for a different series said so is how this fault gets expensive.
The spread is real money. On the SENSEI RX the worst case is $450; on the Non-SENSEI the same number can reach $900. 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. 39), read Aug 2026 — the manufacturer's own documentation for this Rinnai range.
The same number on other brands
Code 34 is not a standard across the industry — every manufacturer publishes its own table. If your unit is not a Rinnai, this number means something else entirely:
Parts, guides and symptoms behind code 34
Everything the 2 Rinnai series point at for this code, in one list. A part named here is one the manufacturer's own procedure reaches for.