Navien E441

What does Navien E441 mean?

E441 means the hot water inlet 2 thermistor has faulted open or short. On dual-heat-exchanger Navien models, this sensor monitors the inlet temperature of the second heat exchanger's hot-side connection. Without a valid reading from this thermistor, the PCB cannot safely control the secondary heat exchanger's temperature and shuts the unit down.

Symptoms

• Unit displays E441 and stops producing hot water.
• Error appears at startup before the burner fires.
• Hot water inlet 2 temperature reading in diagnostics is absent, frozen, or implausible.
• Unit does not recover through reset if the fault is continuous.

Common causes

• Hot water inlet 2 thermistor probe failed open or short.
• Wiring harness connector at the thermistor corroded, loose, or broken.
• Wire insulation damaged near the heat exchanger causing a short to chassis.
• PCB thermistor input channel failure.

Diagnostic steps

1. 01

   Power down the unit and locate the thermistor

   Turn off the unit and cold water supply. Using the NPN-199E wiring diagram, locate the hot water inlet 2 thermistor on the secondary heat exchanger's hot-side inlet pipe.

2. 02

   Inspect the connector for damage

   Disconnect the thermistor's wiring connector and inspect both sides for corrosion on the pins, cracked connector housings, or broken wire leads. Reseat firmly and check latch engagement.

3. 03

   Measure thermistor resistance

   With the connector disconnected, measure resistance across the thermistor terminals and compare to the service manual's resistance-temperature chart. A reading of 0 Ohms or infinite resistance confirms sensor failure.

4. 04

   Check diagnostic value for thermistor K

   Access the Navien diagnostic menu and navigate to the [K] parameter (hot water inlet 2 thermistor value). A frozen, maximum, or zero reading confirms the sensor is not providing a valid signal to the PCB.

5. 05

   Replace the thermistor and verify

   Install the OEM replacement thermistor at the correct immersion position and torque. Reconnect the harness, restore power, and run a full heat call to confirm E441 is cleared and the [K] diagnostic value tracks correctly with temperature.

When to call a professional

If E441 returns after thermistor replacement, a technician should check the PCB's thermistor input circuit with the Navien service diagnostic tool. A failed PCB input channel requires PCB replacement, which involves transferring system configuration and recalibrating temperature offsets — tasks that require authorized service access and Navien's service software.