Utica Dunkirk E125 Error Code

What does Utica Dunkirk E125 mean?

E125 on Utica-Dunkirk DCC/DCB condensing boilers indicates that the control board detected inadequate primary water circulation. Specifically, either the supply temperature failed to rise by at least 2°F within 15–30 seconds after the burner lit, or the supply temperature exceeded the setpoint by 80°F twice within 10 minutes — both symptoms of insufficient flow through the heat exchanger.

Symptoms

• Boiler display shows E125 shortly after burner ignites
• Heat exchanger gets very hot while circulator runs
• No heating output despite burner appearing to operate
• Boiler cycles on and off with E125 appearing repeatedly

Common causes

• Circulator pump seized, wired incorrectly, or running backwards
• Air-locked heating circuit blocking water flow
• Zone valves closed or failed in the shut position
• Incorrect NTC supply or return sensor wiring (supply and return swapped)
• Excessively dirty or scaled heat exchanger restricting flow

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Diagnostic steps

1. Confirm pump operation

   With the boiler powered, listen and feel for vibration at the circulator. A seized pump will be silent and cool; a running pump will hum and warm.

2. Purge air from the heating circuit

   Open auto-vent valves and bleed all radiators or panel coils to remove trapped air that can block water flow and cause temperature spikes.

3. Verify zone valves are open

   Check that at least one heating zone valve is fully open. Manually open zone valves if their actuators are suspected faulty.

4. Check supply and return sensor wiring

   Verify the NTC sensors are installed on the correct pipes — supply sensor on the flow outlet, return sensor on the return inlet. Swapped sensors produce reversed temperature readings that trigger E125.

5. Reset and retest

   Press and hold the RESET button for 2 seconds. Observe whether supply temperature rises steadily within 30 seconds of burner light-off.

When to call a professional

Call a licensed technician if the pump is seized and requires replacement, if the heat exchanger is fouled and needs chemical flush or replacement, or if E125 persists after air purging and valve checks. Pump replacement and system flushing on a pressurized hydronic system require proper tools and isolation procedures to avoid burns and water damage.