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Error code reference

Rheem Water Heater Error Code 33

Faulty outlet thermistor.

Rheem codesRheem water heater codes

Faulty outlet thermistor.

First step from the service manual

Contact a dealer or qualified service technician.

The complete diagnostic procedure includes additional test steps, resistance specifications, wiring diagram references, and component test points.

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What 33 means on a Rheem water heater

Error code 33 on a Rheem water heater indicates a fault with the outlet thermistor, which is the temperature sensor positioned at or near the hot water outlet of the unit. This thermistor continuously monitors the temperature of the water leaving the heater and sends that data as a resistance signal to the control board. The control board uses this reading to regulate heating cycles and ensure safe outlet water temperatures. When the control board detects a signal from the outlet thermistor that falls outside the expected resistance range, it flags error code 33 and may shut down or limit the unit's operation to prevent unsafe conditions.

The most common causes of this fault include a failed thermistor, a wiring harness issue between the thermistor and the control board, or a loose or corroded connector at either end of the circuit. Thermistors are negative temperature coefficient devices, meaning their resistance decreases as temperature increases. If the sensor shorts, opens, or drifts out of calibration, the control board interprets this as an invalid reading and triggers the fault code.

Because diagnosing this error accurately requires checking resistance values across the thermistor at known temperatures and inspecting the wiring harness and control board connections, Rheem recommends contacting a dealer or qualified service technician. Improper handling of internal components can void warranties and, in gas models, may involve risks related to combustion or high-voltage ignition systems.

Source: manufacturer service documentation.

Common causes of 33

  1. 01

    Failed outlet thermistor

    Part replacement

    The thermistor itself may have failed due to age, heat stress, or moisture exposure, causing it to send an out-of-range resistance signal to the control board. A technician can confirm this by measuring the thermistor's resistance and comparing it to the expected value at the current water temperature.

  2. 02

    Loose or disconnected wiring connector

    Wiring / connection

    The connector attaching the thermistor to the wiring harness can loosen over time due to vibration or thermal cycling. Inspecting and reseating the connector at both the thermistor and control board ends may resolve the fault.

  3. 03

    Corroded or damaged wiring

    Part replacement

    Corrosion or physical damage along the wiring harness between the thermistor and the control board can cause resistance readings to become erratic or invalid. A visual inspection of the harness for burn marks, fraying, or corrosion is the first step.

  4. 04

    Faulty control board

    Part replacement

    In some cases, the control board itself may be misreading a signal from a functioning thermistor due to internal board failure. This is typically only diagnosed after confirming the thermistor and wiring check out correctly.

See the test procedure for each cause

Frequently asked questions about 33

What does 33 mean on a Rheem water_heater?
Error code 33 on a Rheem water heater indicates a faulty outlet thermistor. This is the sensor that measures the temperature of the hot water leaving the unit and reports it to the control board. When the sensor's signal falls outside the expected range, the control board registers this fault. A qualified technician should diagnose and service the unit.
Can I fix error code 33 on my Rheem water heater myself?
Rheem recommends contacting a dealer or qualified service technician for this error. Diagnosing the fault correctly involves measuring thermistor resistance values and inspecting internal wiring, which requires technical knowledge and proper tools. Attempting repairs without this expertise could cause further damage or create safety risks, particularly on gas models.
Is it safe to use my Rheem water heater while error code 33 is active?
Error code 33 means the control board cannot reliably confirm outlet water temperature, which could result in inaccurate temperature regulation. Continued use is not recommended until the fault is resolved, as the unit may not properly control heating cycles. Shut down the unit and contact a technician promptly.
How much does it cost to fix error code 33 on a Rheem water heater?
Repair costs vary depending on the root cause. A thermistor replacement is generally an inexpensive part, but total costs including labor typically range from around $100 to $300 or more. If the control board requires replacement, costs can be higher, potentially ranging from $200 to $600 depending on the model and service rates in your area.
Will resetting my Rheem water heater clear error code 33?
Resetting the unit may temporarily clear the error code, but if the underlying thermistor or wiring issue is still present, the fault will return quickly. A reset is not a fix for this error. The thermistor circuit must be properly diagnosed and repaired before the code will clear permanently.

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