E4 is displayed and the unit stops cooling or heating; may restart after some time.

Safety first: Isolate power before working near the outdoor fan or coil.

Steps:

• Clean outdoor coil: Remove leaves, plastic bags, and dirt from the Bosch outdoor condenser. Use a soft brush and low-pressure water spray from inside out if accessible. Do not bend fins.
• Check outdoor fan: Restore power and observe the outdoor fan when the unit calls for cooling. If the compressor runs but the fan does not, or runs very slowly, the fan motor or its capacitor may be faulty.
• Ensure ventilation: Confirm that there is adequate clearance around the outdoor unit as per Bosch installation manual (typically at least 30–50 cm on sides and more at the front). Remove obstructions.

If E4 persists: Overcharge, blocked refrigerant circuit, or a faulty high-pressure sensor/switch may be present. These require a licensed technician to measure pressures, adjust charge, and test/replace the high-pressure protection device.