Rinnai SENSEI Code 25
Condensate pump fault or blocked condensate drain. Condensate has backed up far enough to close the condensate safety switch, or an accessory condensate pump has stopped working. Rinnai notes the code appears when the float switch trips because condensate is not getting away — which on a condensing unit means a clogged, frozen, or badly routed drain line as often as a dead pump.
DIY fixThe verdict
Replace a part
Start with the drain, not the pump. A clogged or frozen condensate line costs nothing to clear and is the most common cause. If the line is clear and the pump has power but does not run, a replacement pump is a modest part — the wiring back to the board is a technician's job.
Typical cost: $0–$350
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. 34), read Aug 2026 — the manufacturer's own documentation for this exact series.
What you can safely check
- Follow the condensate drain line and check it is not kinked, clogged, or frozen where it leaves the building.
- Confirm the drain line still has the air gap it was installed with.
- If a condensate pump is fitted, check it is plugged in and its outlet has power.
- If the drain is clear and the pump has power but does not run, book a service call.
Frequently asked questions
Why does the drain freeze?
Condensate is a slow trickle of water. Where the line runs through an unheated space or terminates outside, a cold snap freezes it solid — which is why this code has a season.
Code 25 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: