Rinnai code 25: condensate drain or pump problem

Condensing Rinnai heaters produce acidic water, called condensate, that must drain away. A float switch watches the level. When condensate backs up, the switch trips and the unit shows code 25.

Code 25 can also appear when an external condensate pump, used where there is no floor drain, stops working.

Rinnai makes several generations of tankless heaters (SENSEI, SENSEI RX/CX and older non-SENSEI models). The meaning below comes from Rinnai's own diagnostic code guide; the exact service steps differ slightly between generations.

What to check

1. The condensate pump, if you have one. Make sure it is plugged in and has power, and listen for it running.
2. The drain line. Follow it from the heater to the drain and look for kinks, sags that hold water, debris or ice.
3. The air gap. Rinnai calls for an air gap where the line enters the drain. A line pushed tightly into a drain pipe can stop flowing.
4. The neutralizer, if installed. A neutralizer packed with spent media can restrict flow.

How to reset it

1. Close all hot water taps.
2. Turn the water heater off at the temperature controller, wait about a minute, then turn it back on.
3. Open a hot tap and watch whether the code returns.

If the same code comes back, the cause is still there. Resetting over and over is not a repair.

When to call a technician

Call a licensed installer if code 25 returns after you have confirmed the external condensate line and any condensate pump are working. The blockage may then be in the condensate trap inside the heater, or the float switch wiring may be damaged, and both are inside the unit.

See the full list on our Rinnai error codes page.