Boiler displays E9 and will not fire, may show abnormal supply temperature reading

Safety first: Turn off power and allow the boiler to cool.

• Locate supply sensor: Identify the supply water temperature sensor on the outlet manifold or top of the heat exchanger on the Utica boiler.
• Check connection: Verify the sensor is firmly seated in its well and the wiring connector is fully engaged at the control board.
• Inspect cable: Look for signs of overheating, melted insulation, or mechanical damage along the sensor cable. Replace if compromised.
• Test sensor: With power off, disconnect the sensor and measure resistance. Compare to the Utica chart. Replace the sensor if readings are not within expected range.
• Control board check: If a known-good sensor still results in E9, the main control board may have a failed sensor input and should be replaced by a technician.