Rinnai Non-SENSEI Code FF
Maintenance performed marker. Not a fault. It 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. If you are reading the code history and find FF, it marks a service visit.
DIY fixThe verdict
No parts needed — reset or re-check a setting
Nothing is wrong and nothing needs doing. If FF is on the display rather than in the history, clear it from the controller.
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 Non-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 fix. If you are reading the code history, FF marks a point where someone recorded a service visit.
Code FF 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: