Rheem code 32: heat exchanger sensor fault

The heat exchanger thermistor tells the control board how hot the heat exchanger is. Without a valid reading, the heater cannot protect itself from overheating, so it shuts down.

This page uses two Rheem sources: the current Rheem and Ruud tankless troubleshooting manual, and Rheem's error code list for earlier tankless models. Codes can differ between generations, so the meaning for each is shown where they differ. Rheem technical support: (800) 432-8373.

What it means by model generation

What a technician does

1. Turns off power and disconnects the thermistor connector on the control board.
2. Measures resistance on the specified wires, which differ between mid-efficiency and high-efficiency models.
3. If the reading is out of range, checks at the sensor itself to tell a bad sensor from a bad harness.
4. Replaces the thermistor, the harness or, rarely, the control board.

Related codes

Rheem heaters have four thermistors: inlet (31), heat exchanger (32), outlet (33) and ambient (34). Code 35 means one of them is not connected properly. Scale can affect sensor readings, so ask whether the unit needs a flush.

How to reset it

1. Close all hot water taps.
2. Turn the remote control off, wait about 10 seconds, then turn it back on.
3. Open a hot tap and watch whether the code returns.

Before you call

Have the model and serial number from the rating label ready, and note whether your unit is a condensing (high-efficiency) or non-condensing model. Tell the technician the exact code, when it appears and any recent work on the gas, water, venting or electrical supply. That often saves a second visit.

See every code on our Rheem error codes page.