Heater display shows E04 and heating is disabled.

Safety first: This fault involves high voltage. Isolate the heater at the main breaker and verify with a meter before opening the unit. If you are not qualified, contact a licensed electrician or pool technician.

• Listen for contactor operation: When the heater calls for heat (before E04 appears), you should normally hear a click from the power contactor. No click or continuous buzzing may indicate a fault.
• Inspect wiring: With power off, remove the cover and inspect the main contactor and associated wiring. Look for burnt insulation, discoloration, or loose terminals. Tighten any loose connections to manufacturer torque specs.
• Check contactor coil: Using a multimeter, test the contactor coil resistance and compare with Elecro specifications. An open coil indicates a failed contactor.
• Control board relay: On models using PCB-mounted relays or SSRs, inspect for visible burn marks or cracking. A failed relay usually requires control board replacement.

Due to the risk of electric shock and fire, replacement of contactors or control boards should generally be performed by a professional.