Rheem Water Heater Error Code 31

Code 31 on a Rheem water heater indicates a fault with the inlet thermistor, the sensor that measures the temperature of cold water entering the unit. The control board has detected a resistance value from the thermistor that falls outside the expected range. This can be caused by a failed thermistor, damaged wiring, or a corroded connector. The unit will not operate normally until the issue is resolved.

Operating the unit with an active code 31 is not recommended. Without accurate inlet temperature data, the control board cannot properly regulate the heating cycle, which may lead to inconsistent water temperatures or unsafe operating conditions. It is best to shut the unit down and have it inspected before resuming use.

Repair costs vary depending on the specific cause. If only the inlet thermistor needs replacement, parts and labor typically range from roughly 100 to 300 dollars. If the wiring harness or control board is also involved, costs can be higher, potentially ranging from 200 to 600 dollars or more depending on parts pricing and local labor rates. Getting a diagnostic assessment from a qualified technician will provide a more accurate estimate for your specific unit.

Rheem advises contacting a dealer or qualified service technician to address code 31. Diagnosing the inlet thermistor requires checking resistance values against specific temperature-resistance specifications and accessing internal components safely. A knowledgeable technician can differentiate between a bad thermistor, wiring fault, or control board issue. Attempting the repair without the proper reference data and tools risks misdiagnosis or additional damage.

A reset may temporarily clear the code display, but if the inlet thermistor or its associated wiring is genuinely faulty, the code will return once the unit attempts to operate and reads the out-of-range signal again. A reset does not fix the underlying hardware problem and is not a substitute for proper diagnosis and repair.