Rinnai code 32: outgoing water temperature sensor fault

A tankless heater adjusts its burner second by second based on how hot the outgoing water is. That reading comes from a thermistor, a small sensor whose electrical resistance changes with temperature. When the reading makes no sense to the control board, the unit shows code 32.

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.

Common causes

• Scale on the sensor. Rinnai's service steps include removing the thermistor and cleaning any buildup off it. In hard water areas, scale is a frequent culprit.
• Loose or damaged wiring between the sensor and the control board.
• A failed sensor. A technician tests it with a meter; its resistance should drop smoothly as it warms.

What a technician does

1. Checks the wiring harness from the sensor to the board.
2. Shuts off the water, drains the unit, removes the sensor and cleans it.
3. Measures its resistance against Rinnai's reference values.
4. Reinstalls it with its O-ring intact, checks for leaks and fires the unit. If code 32 returns, the sensor is replaced.

On some recirculating models Rinnai also lists a check valve in the internal circulation piping as a possible cause.

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.

Preventing it

Because scale plays a part, keeping up with maintenance matters. If you have hard water, plan to descale a tankless water heater about once a year, or as often as your manual recommends.

See the full list on our Rinnai error codes page.