Boiler displays E04 and will not fire; low system pressure warning or water shortage

Safety first: Allow the system to cool before topping up pressure. Do not exceed the maximum pressure indicated in the manual.

Steps to restore pressure:

• Locate the filling loop: On most Dimplex boilers, a braided hose or integrated filling loop is located beneath the boiler. Ensure both isolation valves are closed before starting.
• Top up the system: Slowly open the filling valves and watch the pressure gauge rise to 1.0–1.5 bar (cold). Close both valves firmly once the correct pressure is reached.
• Reset the boiler: Use the reset function on the Dimplex control panel. The E04 code should clear if low pressure was the only issue.
• Check for leaks: Inspect visible pipework, radiators, and the underside of the Dimplex boiler for signs of water. If pressure drops again quickly, there is likely a leak that needs professional attention.

If E04 persists: A technician should test the Dimplex pressure sensor and inspect the expansion vessel and safety valve for faults.