Hewalex pool heater powers on but compressor does not start; display shows E03.

Safety first: Turn off power at the breaker and verify with a meter if you are qualified. High voltage is present inside the unit.

• Check ventilation: Ensure the unit has adequate clearance on all sides and above. Remove any covers, objects, or vegetation blocking airflow around the compressor compartment.
• Inspect supply voltage: Using a multimeter (only if you are trained), verify that the supply voltage at the unit terminals matches the rating on the Hewalex nameplate. Low or fluctuating voltage can cause overload.
• Allow cooling time: Leave the unit powered off for at least 30–60 minutes to allow the compressor thermal protector to reset. Then restore power and attempt a restart.
• Listen for compressor start: If you hear only a click or humming and then E03 returns, the compressor may be seized or the start components may be faulty.
• When to call a technician: A professional should test compressor winding resistance, the thermal protector, and the contactor, and measure start-up current. Replacement of the compressor or overload device requires a qualified technician.