Rinnai SENSEI RX Code FF
Maintenance performed marker. Not a fault at all. FF is a placeholder a service provider enters into the diagnostic code history to record that maintenance or service was carried out, by pressing the UP, DOWN and ON/OFF buttons together. Seeing it in the code history means someone serviced the unit — it does not mean 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 — that is a question for the previous owner or your installer.
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 RX — 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
How do I see the code history on a SENSEI RX?
With the heater off, press and hold the ON/OFF button for 2 seconds and then press the up arrow at the same time. The last nine maintenance codes display in sequence. Repeat to exit.
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.