Troubleshooting Rheem Error Code 32: What It Means & How to Fix

• Technical Difficulty: Intermediate (Requires basic electrical testing knowledge)
• Estimated Time: 45 to 90 Minutes
• Required Tools: Phillips #2 Screwdriver, Digital Multimeter (DMM), Needle-nose pliers, and a clean rag.
• Estimated Repair Cost: $25 – $85 (depending on whether it is a wiring repair or a full thermistor replacement).

Rheem Error Code 32 designates a specific failure within the **Outlet Thermistor** circuit. This component is a Negative Temperature Coefficient (NTC) resistor responsible for communicating the final temperature of the water leaving the heat exchanger to the main control board (PCB). When the PCB detects a resistance value that is mathematically impossible (indicating a short or open circuit) or out of the calibrated safety range, it triggers a hard lockout.

If you are seeing this code, you are likely experiencing a total loss of hot water, as the unit will refuse to ignite the burner for safety reasons. You might also hear the internal fan running as the system attempts a purge cycle before locking out. While a “system failure” sounds daunting, as a senior engineer, I can assure you that this is typically a straightforward sensor replacement or a simple wiring fix that does not require replacing the entire unit.

Troubleshooting & Replacement Instructions

Follow these steps precisely. Safety is paramount; ensure you are comfortable working around electrical components before proceeding.

1. System Isolation and Safety:
   Before opening the cabinet, turn off the electrical power supply to the unit. Do not just turn off the remote; unplug the unit or flip the breaker. Close the gas shut-off valve as an added precaution. WARNING: The internal components may be hot if the unit was recently running. Allow 15 minutes for the heat exchanger to cool.
2. Accessing the Internal Components:
   Use your Phillips head screwdriver to remove the four screws securing the front access panel. Carefully pull the panel forward. Ensure you do not damage the gasket around the edge of the cover, as this maintains the combustion seal.
3. Locating the Outlet Thermistor:
   Look for the copper pipe exiting the bottom of the heat exchanger (the hot water outlet). You will see a small sensor inserted into a brass well or clipped directly to the pipe. It will have two wires (typically white or grey) leading to a plastic connector.
4. Conducting a Resistance Test (The Diagnostic Key):
   Disconnect the thermistor’s plastic molex connector. Set your Digital Multimeter to the Ohms (Ω) setting (20k scale). Place your probes into the connector pins leading to the sensor. At room temperature (approx. 77°F/25°C), you should read roughly 10k to 15k ohms. If the meter reads “OL” (Open Loop) or 0.00 (Short), the sensor is definitively dead and must be replaced.
5. Removing the Faulty Thermistor:
   If the sensor is faulty, remove the retaining clip or screw holding it in place. If it is an immersion-type thermistor, you must shut off the water supply and drain the unit via the drain valves before removal, or water will spray into the electronics. Have a rag ready to catch any residual drips.
6. Installing the New Component:
   Seat the new thermistor into the port. If it uses an O-ring, ensure it is lubricated with a tiny amount of silicone grease (plumber’s grease) to prevent leaks. Reinstall the retaining clip/screw. Reconnect the wiring harness, ensuring the plastic tabs “click” into place.
7. Restoration and Testing:
   Turn the water supply back on and check for leaks at the sensor site. Once dry, restore gas and power. Replace the front cover. Power the unit on and run a hot water tap at high flow. The error should be cleared, and the unit should modulate normally.

Technical Explanation of the Fault

As a Senior Engineer, I categorize the root causes of Error 32 into three primary failure modes. Understanding these is vital for an accurate diagnosis:

1. Component Degradation (NTC Drift): Thermistors operate by lowering their resistance as temperature increases. Over years of thermal cycling (expanding and contracting), the internal ceramic element can crack or “drift.” This drift causes the sensor to report temperatures that are physically impossible, such as 300°F water in a 120°F system, forcing the PCB to trip Error 32 to prevent scalding.
2. Dielectric Breakdown or Corrosion: The outlet thermistor is situated on the hot water pipe. If there is even a microscopic leak at the O-ring seal, moisture can enter the connector housing. This creates a “bridge” between the two wires, causing a short circuit. The PCB sees zero resistance and immediately identifies a shorted thermistor.
3. Wiring Harness Integrity: Tankless units vibrate during high-fire operation. Over time, the wiring harness leading from the thermistor to the PCB can rub against the metal chassis. This abrasion strips the insulation, leading to an intermittent short. Furthermore, rodents are often attracted to the soy-based insulation used in modern wiring, leading to chewed wires that result in an “Open Circuit” (infinite resistance).

Symptoms of a Failing Outlet Thermistor

When Error 32 occurs, the water heater will typically manifest several distinct physical and operational symptoms that go beyond just the digital display:

• Immediate Shutdown: The unit may start for a few seconds, but as soon as the PCB attempts to read the temperature for modulation, the system will kill the flame and flash “32”.
• “Cold Water Sandwich” Effect: In the early stages of thermistor degradation, you may experience fluctuating water temperatures where the water goes from hot to cold intermittently before the error code becomes permanent.
• Diagnostic Lockout: Even after cycling the power, the code may reappear instantly. This indicates a “Hard Fault,” meaning the electrical path is completely severed or shorted to the ground.
• Audible Fan Activity: The combustion fan may run at high RPMs as the unit attempts to cool down the heat exchanger, erroneously believing there is an overheat condition due to the faulty resistance reading.

How to Prevent Error 32

While some component failures are inevitable due to age, you can significantly extend the life of your Rheem’s sensors with these professional maintenance tips:

• Annual Descaling: Scale buildup on the thermistor bulb acts as an insulator, forcing the sensor to work harder and respond slower to temperature changes. Flushing your unit with food-grade white vinegar once a year prevents this “crust” from forming on the probe.
• Install a Surge Protector: The PCB’s sensing circuit is highly sensitive to voltage spikes. A dedicated surge protector for your water heater can prevent “ghost errors” and protect the delicate NTC sensing logic on the board.
• Inspect Seals Yearly: During your annual flush, check the thermistor mounting point for any signs of green oxidation or white mineral powder. Catching a slow leak early prevents the moisture from wicking into the wires and causing a short circuit.

Frequently Asked Questions

Q: Can I bypass the thermistor with a jumper wire just to get a shower?
A: Absolutely not. Bypassing the thermistor removes the system’s ability to regulate heat. This would cause the unit to fire at maximum BTU, potentially boiling the water inside the heat exchanger and causing an explosion or severe scalding. The PCB is programmed to detect jumpers and will throw a different error code (Error 31) if it detects a fixed resistance.

Q: I replaced the thermistor but Error 32 persists. What now?
A: If a new sensor doesn’t fix the issue, the fault lies in the wiring harness or the Main PCB itself. Inspect the entire length of the wire for pinches. If the wires are intact, the “sensing bridge” on the control board has likely failed, and the PCB will need replacement.

Q: Does the Error 32 mean my heat exchanger is cracked?
A: No. Error 32 is strictly an electrical communication fault between the sensor and the board. It does not indicate a structural failure of the heat exchanger, though a leak from the heat exchanger dripping onto the sensor could be a secondary cause.