Utica Dunkirk E110 Error Code

What does Utica Dunkirk E110 mean?

E110 on the Dunkirk DCC/DCB condensing boiler indicates the safety thermostat has tripped due to overtemperature in the heat exchanger. The overheat thermostat is a manual-reset safety device that opens when water temperature at the primary heat exchanger exceeds a safe limit. This is typically caused by blocked water circulation or air in the heating circuit preventing adequate heat transfer.

Symptoms

• E110 displayed live on the boiler control panel — boiler is locked out.
• Boiler does not restart after power cycling — manual reset is required.
• Heat exchanger may be hot to the touch on the case exterior.
• System pressure may be elevated if overheating caused steam formation.

Common causes

• Circulator pump blocked, seized, or not running — most common cause.
• Air trapped in the heating circuit reducing effective water flow through the heat exchanger.
• Faulty safety thermostat or damaged thermostat cable giving a false trip.
• System zone valves or isolating valves partially or fully closed, restricting flow.

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Diagnostic steps

1. Allow the boiler to cool

   Do not attempt to reset immediately. Allow the heat exchanger to cool completely before inspecting or resetting — at least 15–20 minutes after shutdown.

2. Check and restore water circulation

   Verify the circulator pump is running. Check for air in the circuit by bleeding radiators and system high points. Confirm all zone valves and isolating valves are fully open.

3. Inspect the safety thermostat and cable

   Locate the safety thermostat on the primary heat exchanger. Check the cable and connector for physical damage. Measure continuity across the thermostat — resistance greater than 1.5 ohm after cooling indicates a failed thermostat that must be replaced.

4. Reset the boiler

   After the boiler has cooled and circulation issues have been corrected, hold the reset button for at least 2 seconds to clear the E110 lockout.

5. Monitor for recurrence

   Run the boiler through a full heating cycle and monitor the supply and return temperatures to confirm the temperature differential is within normal limits and E110 does not recur.

When to call a professional

Call a licensed technician if E110 recurs after pump inspection and air purging, or if the safety thermostat requires replacement. Overtemperature events that repeat without a clear cause indicate a circulation design problem or heat exchanger scaling that requires professional diagnosis. Continued operation with an unresolved overtemperature condition risks heat exchanger damage.