Navien E432 Error Code

What does Navien E432 mean?

E432 indicates the cold water inlet 2 thermistor has faulted open or short. On multi-heat-exchanger Navien models, a second cold water inlet thermistor monitors the second heat exchanger's inlet temperature independently. When this sensor's signal falls outside the valid resistance window, the PCB logs E432 and shuts down the unit to prevent uncontrolled water heating.

Symptoms

• Unit shuts off with E432 displayed; no hot water produced.
• Error appears at startup or early in the heating cycle.
• Cold water temperature reading in diagnostics shows an implausible value or none.
• Unit does not respond to reset if the thermistor fault is hard.

Common causes

• Cold water inlet 2 thermistor probe failed open or short.
• Wiring harness connector corroded or disconnected at the second inlet thermistor location.
• Wire insulation damaged near the heat exchanger, causing a short to chassis.
• PCB thermistor input circuit failure on the second channel.

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Diagnostic steps

1. Power down and locate inlet 2 thermistor

   Turn off the unit and water supply. Using the wiring diagram for your model, identify the cold water inlet 2 thermistor — on dual-heat-exchanger NPN models it is mounted on the secondary heat exchanger's cold-side inlet pipe.

2. Inspect the connector and wire run

   Disconnect and inspect the thermistor's wiring connector for corrosion, bent pins, and secure latching. Trace the wire run from the thermistor to the PCB harness junction, looking for chafing or heat damage.

3. Test resistance across the thermistor

   Measure resistance with a multimeter and compare to the service manual's resistance-temperature table at current ambient temperature. Zero Ohms (short) or infinite (open) confirms sensor replacement is required.

4. Check diagnostic mode reading

   Enter the Navien diagnostic menu and look for the cold inlet 2 temperature parameter. A reading stuck at maximum, minimum, or 0 confirms the sensor is not providing a valid signal.

5. Replace the thermistor and retest

   Install the OEM replacement thermistor at the correct immersion position. Reconnect the harness, restore power, and confirm through a live heat call that E432 no longer appears and the temperature reading tracks correctly.

When to call a professional

If E432 clears but returns intermittently, suspect a hairline wire break that only opens under thermal expansion. Tracing intermittent wiring faults and PCB channel diagnosis require a technician with access to the Navien service diagnostic tool and wiring harness specifications. Contact Navien Technical Support at 1-800-519-8794 for parts and model-specific guidance.