Boiler shows E8 and shuts down, often after running for a short period

Safety first: Turn off power and allow the boiler to cool before touching any piping or sensors.

• Locate return sensor: Find the return water temperature sensor on the return manifold or pipe entering the Utica boiler. It may be inserted into a well or strapped to the pipe.
• Check attachment: Ensure the sensor is fully inserted into its well and secured. A loose sensor can read incorrectly and trigger E8.
• Inspect wiring: Follow the sensor leads back to the control board. Look for cuts, abrasions, or loose connectors. Reseat the plug on the board.
• Measure resistance: With power off, disconnect the sensor and measure resistance with a multimeter. Compare to Utica's temperature/resistance chart for the approximate water temperature. Replace if readings are open, shorted, or far off spec.
• Reset and test: After repair or replacement, restore power and reset the boiler. Monitor return temperature readings on the display if available.