Boiler shuts down with E04; display may indicate overheat or high limit

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

• Check system pressure and valves: Verify the hydronic system pressure on the boiler gauge (typically 12–20 psi for residential systems when cold). Ensure all supply and return isolation valves near the Crown boiler are fully open.
• Verify circulator operation: During a call for heat, feel the system circulator pump (mounted on the supply or return piping). It should vibrate slightly and the connected pipes should gradually warm. If the pump is silent and cold, check its electrical connection and fuses. A failed circulator can cause rapid overheating.
• Bleed air from system: If some radiators or zones are cold, bleed air from manual air vents or use automatic air vents on the Crown boiler manifold. Air pockets can stop flow and cause localized overheating.
• Inspect high limit sensor wiring: Locate the high limit/temperature sensor on the boiler outlet or heat exchanger. Ensure the sensor is firmly seated and wiring is intact.
• Reset: After the boiler has cooled, reset the lockout per the Crown manual. If E04 recurs, have a technician test the circulator, high limit sensor, and flow through the heat exchanger.