Utica Dunkirk E43 Error Code

What does Utica Dunkirk E43 mean?

E43 on the Dunkirk DMG-240 means no temperature difference was detected between the supply and return lines during normal burner operation. With the burner on, the supply water should become measurably warmer than the return. If the temperature sensors detect no differential, the control concludes that water is not circulating through the heat exchanger and shuts down the boiler to prevent overheating.

Symptoms

• E43 displayed on the DMG-240 control panel — burner shuts down during a heating call.
• Supply and return water temperatures read the same value on the control display.
• Possible overheating noise or thermal expansion sounds before shutdown.
• Boiler restarts but faults again shortly after burner ignition.

Common causes

• Circulator pump seized, impeller blocked, or wired incorrectly and not running.
• Air lock in the system blocking flow through the heat exchanger.
• Supply or return NTC temperature sensor wiring plug is loose or not inserted into the pipe fitting correctly.
• Supply or return NTC sensor has failed and is reading a fixed or incorrect value.

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Diagnostic steps

1. Confirm the onboard pump is operating

   With a demand for heat, check whether the supply pipe becomes warmer than the return. If the pump is running correctly, supply should warm faster. A pump that is not running will show equal temperatures.

2. Check temperature sensor wire plugs

   Inspect the wiring harness plugs on both supply and return sensors. Firmly reseat any plug that is loose or partially disconnected.

3. Verify sensors are properly inserted in pipe lines

   Confirm both supply and return sensors are fully inserted into their respective pipe pockets or immersion fittings. A sensor not in contact with the pipe will read ambient temperature instead of water temperature.

4. Bleed air from the system

   If air lock is suspected, use the manual air vent and system bleed points to purge air. Check system pressure and refill if needed.

5. Test sensor resistance and replace if faulty

   Disconnect each NTC sensor and measure resistance. Cross-reference readings against the temperature-resistance chart (Figure 13-1 in the IOM). Replace any sensor outside the published range.

When to call a professional

Call a licensed technician if the circulator pump is not running after wiring inspection, if the pump needs replacement, or if persistent air in the system cannot be resolved with manual bleeding. Heat exchanger damage from dry-firing is possible if E43 is not promptly resolved — a technician should inspect the heat exchanger if overheating is suspected.