Water heater shows E04 and stops heating; may occur during long draws of hot water

Critical safety: Overheat conditions can be dangerous. Turn off power and allow the unit to cool completely before touching internal parts.

• Check water flow: Ensure all isolation valves are fully open. Clean inlet filters and shower heads/aerators to restore proper flow.
• Reset safety thermostat: Remove the front cover. Locate the manual reset overheat thermostat on the heat exchanger or tank. Press the small reset button (if present) until it clicks.
• Inspect for scale: Look for heavy limescale on the heat exchanger surfaces or in the inlet. If scale is visible, the unit may need descaling with an appropriate descaling pump and solution, following Dimplex guidelines.
• Test operation: Restore power and run hot water while monitoring temperature. If E04 recurs quickly, the thermostat or control logic may be faulty.

Call a professional: If the safety thermostat trips repeatedly, have a qualified technician check the heat exchanger, thermostat, and control PCB. Do not bypass or short any safety devices.