Utica Dunkirk E28

What does Utica Dunkirk E28 mean?

E28 on Utica-Dunkirk DCC/DCB condensing boilers indicates a fault with the flue NTC heat exchanger temperature sensor. The control board cannot read a valid temperature from this sensor, which monitors flue gas or exhaust-side heat exchanger temperature. The boiler shuts down because the sensor is essential to detecting flue over-temperature and triggering the high-limit function.

Symptoms

• Boiler display shows E28 and enters lockout
• No heating or domestic hot water output
• Fault appears immediately on startup or mid-cycle
• Boiler does not reset automatically

Common causes

• Failed or open-circuit flue NTC sensor
• Loose or disconnected wiring connector at the sensor or PCB
• Damaged sensor lead wire (chafed, kinked, or burned by flue heat)
• PCB input failure on the flue sensor channel

Diagnostic steps

1. 01

   Inspect sensor wiring and connectors

   Locate the flue NTC sensor on the exhaust section of the heat exchanger. Reseat the wiring connector firmly and check for heat damage to the cable insulation.

2. 02

   Measure sensor resistance

   Disconnect the sensor and measure resistance at ambient temperature. Verify the reading against the NTC resistance chart in the IOM; an open reading confirms sensor failure.

3. 03

   Replace the flue NTC sensor

   Install an OEM replacement sensor, ensuring the sensor body seats fully into the flue sensor pocket. Reconnect the wiring harness and inspect for heat damage to nearby components.

4. 04

   Reset the boiler

   Press and hold the RESET button for at least 2 seconds, then run the boiler through a complete heating cycle to confirm E28 does not return.

5. 05

   Contact technical service if fault persists

   If E28 recurs after sensor replacement, the PCB flue sensor input circuit may be defective. Contact Utica-Dunkirk at 1-800-325-5479.

When to call a professional

Call a licensed technician if you are not able to safely access the flue side of the heat exchanger or if the fault persists after sensor replacement. The flue NTC position requires working near hot exhaust components, and PCB replacement requires full recommissioning including combustion calibration — both tasks that require a qualified technician.