Boiler shows E11, pressure gauge indicates high pressure (often above 3 bar), safety valve may discharge water.

Safety: Hot water may discharge from the safety valve. Allow the system to cool before working on it.

• Check filling loop: Ensure both valves on the filling loop are fully closed and that any flexible hose is removed if required by local regulations.
• Reduce pressure: Bleed water from a radiator or drain point until the pressure gauge drops to around 1.2 bar when cold.
• Check expansion vessel: Locate the Defro expansion vessel (often at the rear or side of the boiler). Tap it: a solid sound may indicate it is full of water. With the system depressurized and isolated, check the air charge at the Schrader valve using a tire gauge. It should match the boiler specification (commonly around 0.8–1.0 bar). If low, recharge with a hand pump.
• Monitor pressure: Refill the system to correct pressure and run the boiler. If pressure still rises excessively when hot, the expansion vessel diaphragm may be ruptured and the vessel must be replaced by a technician.