Utica Dunkirk E178 Error Code

What does Utica Dunkirk E178 mean?

E178 appears in the fault history when the low-temperature thermostat connected to input CN2 cuts out, or when the flue pressure switch contact is detected open. The boiler shuts down the burner and logs the event. This anomaly is recorded rather than displayed live; retrieve it through the installer fault-history menu.

Symptoms

• Burner shuts off mid-cycle without a visible live fault on the display.
• E178 appears when scrolling through the installer fault-history log.
• No heat output even though the boiler control board is powered and not in lockout.
• Boiler restarts normally after the thermostat contact closes or flue pressure switch resets.

Common causes

• Low-temperature thermostat on CN2 has opened due to floor-heating system setpoint being reached.
• Flue pressure switch contact is open due to blocked or partially obstructed vent pipe.
• Flue pressure switch wiring harness loose or disconnected.
• Condensate in flue duct creating back-pressure that trips the pressure switch.

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Diagnostic steps

1. Access the fault history

   Enter the installer menu and navigate to the fault-history log to confirm E178 is recorded and note the sub-status, fan speed (nf), and operating hours (hr) at the time of occurrence.

2. Check parameter P07 setting

   If P07 = 04, CN2 is configured for a low-temperature thermostat. Verify that the thermostat is operating correctly and that its setpoint is appropriate for the system.

3. Inspect the flue pressure switch and wiring

   Locate the flue pressure switch, disconnect and re-seat the wiring connector, and check for continuity across the switch terminals when the flue is clear and the fan is running.

4. Inspect the flue duct for obstruction

   Visually check the vent terminal and flue pipe for blockages, bird nests, ice, or condensate buildup that could cause reduced draft and trip the pressure switch.

5. Replace the flue pressure switch if faulty

   If the switch fails a continuity test with a clear flue, replace it with the manufacturer-approved part and re-test system operation.

When to call a professional

Call a licensed technician if flue pressure switch replacement does not clear the code, if you suspect flue gas recirculation, or if the vent system needs modification. Working inside a condensing boiler's sealed combustion system and adjusting parameter P07 requires factory training. Incorrect vent configuration can create a carbon monoxide hazard.