Control panel shows E04 and pump will not start; sometimes appears after water exposure to the control box.

Safety first: Disconnect power at the outlet. Never open the control box while it is connected to mains.

• Inspect for moisture: Open the external cover of the Bestway control panel (if user‑serviceable). Look for signs of condensation, water droplets, or corrosion. If wet, leave the unit open in a dry, shaded area for 24–48 hours to dry completely. Do not use heat guns or hair dryers directly on electronics.
• Check cable connections: Verify that the low‑voltage control cable between the pump and control panel is fully seated at both ends. Gently unplug and replug the connectors to wipe oxidation from the contacts.
• Check for visible damage: Look for burnt spots, cracked solder joints, or green/white corrosion on the PCB. If present, the board is likely damaged.
• Reassemble and test: Once fully dry and reconnected, restore power and check if E04 clears. If the error persists, the control PCB or cable may need replacement.

Because control boards are safety‑critical, replacement should follow Bestway specifications and may require a qualified technician.