Rinnai error code FF
Maintenance performed marker. Code FF means the same thing on all 3 Rinnai series documented here — but the fix, and what it costs, is still worth reading for your exact unit.
What code FF means on each Rinnai series
| Series | What it means | Verdict | Typical cost |
|---|---|---|---|
| Non-SENSEI | Maintenance performed marker | DIY fix | $0–$0 |
| SENSEI | Maintenance performed marker | DIY fix | $0–$0 |
| SENSEI RX | Maintenance performed marker | DIY fix | $0–$0 |
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 FF routes it the same way: clear it yourself. 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 cost is documented the same way across all 3 series: $0–$0, depending on which of the manufacturer's causes turns out to be yours.
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. 64), read Aug 2026 — the manufacturer's own documentation for this Rinnai range.