Boiler control display shows E0 and burner will not start

Safety first: Turn off power to the boiler at the service switch and shut off gas supply before removing any panels. Allow components to cool.

• Access the control area: Remove the front jacket panel to access the main control board and wiring harness on the Utica boiler.
• Locate the outdoor sensor: Find the outdoor temperature sensor (often a small probe mounted on an exterior wall, wired back to the boiler's low-voltage terminal strip labeled "ODT" or "Outdoor Sensor").
• Inspect wiring: Check the two-conductor cable from the outdoor sensor to the boiler. Look for cuts, crushed insulation, loose wire nuts, or corroded terminals. Tighten any loose connections and repair damaged cable.
• Test sensor resistance: With power still OFF, disconnect the sensor leads at the boiler. Use a multimeter set to ohms and measure resistance across the sensor. Compare to the Utica temperature/resistance chart in the installation manual. If reading is open (OL) or near 0 ohms, the sensor is defective.
• Bypass test: Temporarily substitute a known-good NTC sensor of the same spec or a fixed resistor value recommended by Utica to see if the E0 clears when power is restored. Do not operate long-term with a bypass.
• Restore power and test: After repairing wiring or replacing the outdoor sensor, restore power and clear the error by cycling power. Verify the display now shows a reasonable outdoor temperature and the burner can start.
• If fault persists: If wiring and sensor test good, the outdoor sensor input on the main control board may be defective. Replacement of the control board should be performed by a qualified technician.