Boiler shows E4 and shuts down before or during ignition

Safety first: Turn off power and gas. Flue components may be hot and flue gas can be hazardous.

• Inspect venting system: Follow the PVC/CPVC/PP vent and intake pipes from the Utica boiler to the outside. Look for sags holding condensate, disconnections, or crushed sections. Correct any visible issues.
• Check termination: Outside, verify that the vent and intake terminations are not blocked by snow, leaves, nests, or debris. Clear any obstructions and maintain required clearances per Utica manual.
• Examine flue temperature sensor: Locate the flue gas temperature sensor (usually clipped to or inserted into the exhaust outlet near the heat exchanger). Inspect wiring and connector. If the sensor is loose from the flue surface, reattach securely.
• Test sensor continuity: With power off, disconnect the flue sensor and measure resistance with a multimeter. Compare to Utica's temperature/resistance chart. Replace if open, shorted, or far out of range.
• Reset and test: Restore power and gas, reset the boiler, and observe operation. If E4 recurs quickly, vent design or combustion issues may exist and require a professional with combustion analysis tools.