Rinnai SENSEI Code FF
Maintenance performed marker. Not a fault. FF is a placeholder a service provider enters into the diagnostic code history to record that maintenance or service was carried out, by pressing UP, DOWN and ON/OFF together. Seeing it means someone serviced the unit — not that anything is wrong.
DIY fixThe verdict
No parts needed — reset or re-check a setting
Nothing to fix and nothing to pay for. If FF is in your code history, it is a bookmark left by whoever last serviced the heater. It is only worth a second look if you have no record of any service.
Typical cost: $0–$0
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 SENSEI — not averaged across the brand.
Source: Rinnai Troubleshooting Tankless Water Heater Diagnostic Codes (100000652) (p. 64), read Aug 2026 — the manufacturer's own documentation for this exact series.
What you can safely check
- Nothing to do. FF marks service, not a fault.
- If it appears alongside a real code, deal with that code — FF is not the cause.
Frequently asked questions
Should I enter FF myself after flushing the unit?
It is what the code is for — Rinnai describes it as a placeholder entered after performing service, using UP, DOWN and ON/OFF together. Keeping the history honest helps whoever works on it next.
Code FF on other Rinnai series
Other Rinnai series report code FF under the same fault name, but each manual is transcribed separately and they do not read alike: