Boiler displays E3 and will not fire, circulator may run

Safety first: Turn off power and allow the boiler to cool completely. System water may be very hot.

• Check system pressure and flow: Verify the system pressure on the boiler gauge is within Utica's recommended range (typically 12–20 psi for residential hot water). Ensure isolation valves on the supply and return piping are open.
• Verify circulator operation: With power restored, call for heat and listen/feel for the system circulator pump (e.g., Grundfos or Taco pump mounted on the boiler piping). If it does not run, check the pump's electrical connection and any external pump relay. A seized pump can cause rapid temperature rise.
• Inspect high limit sensor: Locate the supply water temperature sensor or high limit probe on the boiler's supply header or heat exchanger. Check wiring for damage or loose connectors. Reseat the plug on the control board.
• Bleed air from system: Air-bound zones can reduce flow and cause overheating. Use manual air vents or automatic air eliminators on the Utica boiler and near radiators to purge trapped air.
• Reset and monitor: After restoring flow and verifying sensors, reset the boiler. Monitor supply temperature on the display; if it climbs rapidly to limit, the heat exchanger or piping may be restricted and should be inspected by a technician.