Heater displays E04 and will not fire; may occur immediately after start command

Safety first: Turn OFF power to the heater before opening panels. Water-side checks can be done with pump running but keep hands clear of moving parts.

• Verify pump operation: Ensure the pool circulation pump is running and primed. Check for air in the pump basket and correct any suction leaks.
• Clean filtration system: Backwash or clean the pool filter according to the manufacturer instructions. Empty skimmer and pump baskets.
• Check valves: Confirm that all valves to and from the Poolworld heater are fully open and that bypass valves are correctly positioned to allow adequate flow through the heater.
• Inspect pressure switch: Locate the water pressure switch on the inlet/outlet header. With power OFF, inspect wiring connections. If accessible, gently tap the switch body to free a stuck diaphragm.
• Flow test: After restoring flow, turn power back on and call for heat. If E04 persists despite strong water flow, the pressure switch may need adjustment or replacement.

Warning: Never bypass the pressure switch permanently; it is a critical safety device that prevents dry firing and heat exchanger damage.