Utica Dunkirk E06

What does Utica Dunkirk E06 mean?

E06 on the Utica-Dunkirk DMG-240 condensing boiler indicates the return water temperature sensor has a short circuit — the sensor reads near-zero resistance, which the control board interprets as an impossibly high return temperature. The boiler locks out because it cannot safely monitor the return circuit without a valid sensor reading, which is essential to differential temperature and circulation control logic.

Symptoms

• Boiler display shows E06 on startup or mid-cycle
• Return temperature reading on the display is erroneously high or missing
• Boiler locks out and cannot be cleared by reset alone
• Fault is persistent if the sensor is truly shorted

Common causes

• Return NTC sensor internal short circuit (sensor failure)
• Return sensor harness shorted — conductors pinched together or grounded
• Moisture or condensate ingress at the return sensor connector
• Sensor body grounding to metallic pipe fitting

Diagnostic steps

1. 01

   Disconnect and test return sensor resistance

   Disconnect the return NTC sensor connector and measure resistance across the sensor terminals. A near-zero or very low reading at ambient temperature confirms the sensor is shorted.

2. 02

   Inspect the wiring harness for damage

   Trace the return sensor harness from the sensor to the PCB and look for pinched sections, abraded insulation, or corroded connectors that could cause a short.

3. 03

   Check the sensor connector for moisture

   Dry and clean the sensor connector and PCB header. Condensate near the heat exchanger is common and causes conductive shorts at connectors.

4. 04

   Replace the return NTC sensor

   Install an OEM replacement return NTC sensor, seat it fully in the return pipe pocket, and reconnect the harness. Confirm resistance at ambient temperature matches the NTC curve.

5. 05

   Reset and confirm operation

   Press RESET for 2 seconds and verify the return temperature reading rises appropriately during a heating cycle. E06 should clear after a valid sensor is installed.

When to call a professional

If E06 returns after sensor replacement, the PCB return sensor input circuit is shorted and requires PCB replacement. PCB replacement must be performed by a qualified technician and followed by the full automatic and manual calibration commissioning sequence. Do not continue resetting without addressing the root cause, as uncorrected sensor faults can mask real overheat conditions.