Rinnai SENSEI RX Code 25
Condensate pump fault or blocked condensate drain. Condensate has backed up far enough to close the condensate safety switch, or the 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 like the SENSEI RX 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 accessory pump has no power or does not run, a replacement pump is a modest part — but the wiring back to the PC 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 RX — 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 at the point it leaves the building.
- Confirm the drain line has the air gap it was installed with, and that it runs continuously downhill where it should.
- If a condensate pump is fitted, check it is plugged in and that 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
My unit does not have a condensate pump. Can I still get code 25?
Yes. Rinnai's description covers the condensate safety switch closing when condensate backs up, whether or not an accessory pump is part of the installation.
Why does the drain freeze?
Because condensate is a slow trickle of water. Where the line runs through an unheated space or terminates outside, a cold snap is enough to freeze it solid — which is why this code has a season.
Is the condensate harmful?
It is mildly acidic, so it belongs in the drain it was plumbed to, not on the floor. If you find it pooling, that is a plumbing problem to fix, not just a code to clear.