Rinnai Code 25: Condensate Drain or Pump Fault
On this page (4 sections)
The Short Answer: Rinnai code 25 appears when condensate cannot drain. According to Rinnai, it is triggered by a float (safety) switch that trips when condensate backs up, and it can also occur when an external condensate pump stops working. Check that the pump has power and is pumping, that the drain line is not clogged or frozen, and that the line ends with an air gap. Then restart once.
Why condensing heaters need a clear drain
High-efficiency condensing Rinnai models pull so much heat from the exhaust that water vapor condenses inside the heater. That slightly acidic water has to leave through a trap and drain line, flowing downhill on its own or through a small pump. When it cannot, the water rises, the float switch closes, and the heater stops with code 25. Rinnai’s guide explains this on its code 25 page (opens in a new tab).
A full trap can also cause code 10 on SENSEI models, so you may see either number from the same blocked drain.
Rinnai’s checklist, and who does each step
| Rinnai’s check | Who | What it looks like |
|---|---|---|
| Confirm power to the condensate pump | Owner | Pump plugged in, outlet working, GFCI not tripped |
| Check pump operation | Owner can observe | Reservoir empties when it fills; if the reservoir is full and the motor is silent, the pump has failed |
| Drain line not clogged or frozen | Owner | No kinks, sags holding water, or ice where the line exits the house |
| Drain line has an air gap | Owner can observe; installer corrects | The line should end above the drain opening, not pushed down into it |
| Wiring to the float switch and pump | Technician | Loose, damaged, or broken connections inside the cabinet |
Thaw a frozen outdoor drain line with warm air or warm water on the outside of the tube, never an open flame. After the drain flows, turn the heater off and on once.
Signs it needs a technician
Book a technician if code 25 returns after the drain and pump are working, if you see water inside the cabinet or on the control board, or if the condensate pump fills quickly when no hot water has been used. A pump that fills with no burner operation may be collecting water from a different leak.
A replacement condensate pump or a rerouted drain line is a minor repair. Condensate-related codes do not, on their own, indicate a failed heat exchanger.
Related: water at a Rinnai exhaust after shutdown and a tankless leaking from the bottom.
Frequently Asked Questions
Q: Is water dripping from the condensate line a leak? A: No. On a condensing heater, water from the condensate drain while the burner runs is normal. Water from the cabinet, fittings, or relief valve is not condensate.
Q: Can a non-condensing Rinnai show code 25? A: Code 25 relates to the condensate system of condensing models. If your heater is a non-condensing model with a metal vent and you see 25, confirm the reading and look it up in your model’s manual.
Manuals and supporting references
These links distinguish general safety information from model-specific documentation. A manual directory helps you locate your unit’s instructions; it does not establish that every model uses the same parts, codes, or test values.
- Rinnai: Troubleshooting Tankless Water Heater Diagnostic Codes (100000652), code 25 (opens in a new tab)Rinnai SENSEI and non-SENSEI condensing tankless models listed in the document.
- Rinnai: RSC SENSEI installation and operation manual (100000773), section 5.6 (opens in a new tab)Rinnai RSC SENSEI models; lists code 25 as Condensate Pump (Accessory).
- Rinnai: official document library (opens in a new tab)Select your exact model and owner manual before interpreting a fault or reset procedure.
- A. O. Smith technical bulletin 15: condensation (opens in a new tab)Why combustion condensate can resemble a tank leak; not a diagnosis of another manufacturer’s model.
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