Navien E006 Error Code — What It Means
The E006 error indicates a heating supply outlet thermistor short fault. The control board is detecting a short circuit condition at the outlet temperature sensor input, so it cannot trust the supply outlet temperature signal and shuts down to protect the system. This thermistor monitors the hot water leaving the heat exchanger, and a shorted sensor circuit prevents the unit from regulating temperature safely.
The error appears on the display panel when the sensor circuit reads as shorted, either from a failed thermistor, damaged wiring, or moisture intrusion at the connections. The unit will not fire or produce hot water until the fault is resolved and the board can read valid temperature data from the outlet sensor.
Common Causes
- Failed outlet thermistor The heating supply outlet thermistor itself has developed an internal short circuit and sends a fault signal to the control board.
- Loose or corroded connector The thermistor plug or harness connection has backed out, corroded, or oxidized, creating an intermittent or permanent short at the pins.
- Water or moisture contamination Condensate, leak spray, or humidity has entered the sensor connector or junction box and is bridging the circuit.
- Damaged sensor wiring The thermistor harness has been pinched, chafed, or cut, causing the conductors to short together or to ground.
- Control board input fault The main PCB thermistor input circuit has failed and incorrectly reads the sensor as shorted even when the sensor and wiring are good.
Step-by-Step Fix
- Turn off power at the breaker or disconnect switch and close the gas isolation valve to make the unit safe for inspection.
- Note the error code on the display and confirm it is E006, then open the front cover to access the internal wiring and sensors.
- Locate the heating supply outlet thermistor on the heat exchanger outlet pipe (it will have a two-wire connector and may be secured with a spring clip or bracket).
- Inspect the thermistor connector for looseness, corrosion, moisture, or discoloration, then disconnect the plug and dry or clean both halves if any contamination is present.
- Check the thermistor wiring from the sensor body back to the control board for pinches, cuts, or melted insulation, and repair or replace the harness if damage is found.
- Test the thermistor continuity with a multimeter set to ohms (consult your model’s service manual for the expected resistance range at room temperature), and replace the sensor if it reads zero ohms or open circuit when it should show a specific resistance.
- Reconnect everything, restore power and gas, then run a test cycle and verify the E006 fault clears and the unit heats normally without re-triggering the error.
Parts Often Needed
| Part | Notes |
|---|---|
| Heating Supply Outlet Thermistor | Amazon | Verify your exact Navien model number (NPE, NCB, NFB series) to order the correct sensor with matching connector and thread. |
| Thermistor Wiring Harness | Amazon | Only needed if the original harness is cut, melted, or too corroded to clean and reuse. |
When to Call a Pro
Call a licensed technician if you are not comfortable working with live gas appliances, if the thermistor and wiring both test good but the error persists (indicating a control board fault), or if the error returns immediately after replacing the sensor. A qualified service tech can perform board-level diagnostics, verify proper thermistor resistance values against your model’s specification table, and safely handle any gas or venting issues discovered during the repair. If your unit is still under warranty, professional service may be required to preserve coverage.