Utica Dunkirk E07

What does Utica Dunkirk E07 mean?

E07 on the Utica-Dunkirk DMG-240 condensing boiler indicates the return water temperature sensor has an open circuit — the sensor reads infinite or very high resistance, which the control board interprets as an absence of signal. Without a valid return temperature reading, the boiler cannot manage differential temperature control or verify safe return conditions, so it locks out.

Symptoms

• Boiler display shows E07 on startup or during a heating cycle
• Return temperature display reads zero, very low, or shows dashes
• Boiler locks out before or during ignition
• Fault may be intermittent if the connector is loose

Common causes

• Return NTC sensor failed open-circuit (broken sensing element)
• Return sensor connector unplugged or a pin has pulled out
• Broken wire in the harness between the return sensor and PCB
• Sensor not correctly seated in the return pipe pocket

Diagnostic steps

1. 01

   Reseat the return sensor connector

   Firmly reseat the return NTC sensor connector at both the sensor and PCB ends. An open-circuit E07 on an existing installation is frequently caused by a vibrated-loose connector.

2. 02

   Measure return sensor resistance

   Disconnect the sensor and measure resistance. An OL (open circuit) reading confirms the sensor element has failed and requires replacement.

3. 03

   Flex-test the wiring harness

   Flex the harness along its full length while monitoring resistance with a multimeter. A resistance spike during flexing locates an intermittent break in the wire.

4. 04

   Confirm sensor is fully inserted in the pipe pocket

   The return sensor must be fully seated in its pipe pocket and clamped so it contacts the pipe wall. An air gap causes a falsely high resistance reading.

5. 05

   Replace the return NTC sensor

   Install an OEM replacement return NTC sensor, firmly seat it in the return pipe pocket, and reconnect the harness. Verify resistance at ambient temperature before powering up.

When to call a professional

Call a licensed technician if E07 persists after sensor replacement, indicating a PCB return sensor input fault. PCB replacement requires the full commissioning calibration sequence and should only be performed by a qualified technician. If you are uncertain about safely accessing wiring inside the boiler cabinet, contact an authorized Utica-Dunkirk service professional.