Boiler displays E10, pressure gauge shows low or zero, boiler will not start.

Safety: Allow the system to cool before topping up pressure. Do not exceed the maximum pressure indicated on the gauge.

• Top up system: Locate the filling loop on the Defro boiler or nearby pipework. Open the valves slowly until the pressure gauge reaches the recommended cold pressure (usually 1.0–1.5 bar). Close both valves fully afterward.
• Bleed radiators: Starting from the highest radiators, bleed air using a radiator key. Recheck and adjust pressure as needed.
• Check for leaks: Inspect visible pipework, radiator valves, and the underside of the Defro boiler for signs of water. If pressure drops repeatedly, a leak must be found and repaired.
• Reset boiler: Once pressure is stable, reset the boiler. If E10 persists despite correct pressure, the Defro pressure sensor or switch may be faulty and require replacement.