Safety: Disconnect power at the main breaker. Verify with a multimeter that no voltage is present.

Diagnostic steps:

Check for ground fault: Disconnect the wires from the heating element. Measure resistance between each element terminal and the metal flange (ground). Any low resistance (under several megaohms) indicates a ground fault and the element must be replaced.
Inspect wiring harness: Look for melted insulation, pinched wires, or signs of arcing between the control board and the element terminals.
Visual PCB inspection: Remove the control cover and inspect the control PCB for burned tracks, cracked solder joints, or a visibly damaged triac/relay.
Test with element disconnected: With the element disconnected and covers in place, briefly power the unit. If E04 persists, the control board is likely faulty.
Replace defective parts: Replace the heating element assembly if it is shorted. If the element is good but E04 remains, the control PCB / power module must be replaced as a unit.

Note: Board-level repair (component soldering) should be done only by qualified electronics technicians.

Eldom water heater shows E04 and does not heat; sometimes accompanied by clicking relays.

Possible Causes