Boiler shows E10, pressure gauge indicates high pressure (often above 3 bar), safety valve may discharge water.

Safety: High pressure can cause the safety valve to discharge hot water. Avoid touching discharge pipework.

• Check filling loop: Ensure the Thermona filling loop valves are fully closed and the flexible hose (if removable) is disconnected to prevent accidental filling.
• Reduce pressure: Bleed water from a radiator or drain point until the pressure gauge reads around 1.2–1.5 bar when cold.
• Expansion vessel pre-charge (engineer level): Isolate the boiler and drain pressure from the system. Measure the air charge at the expansion vessel Schrader valve. Recharge to the value specified by Thermona (commonly around 0.8–1.0 bar) using a hand pump.
• Check vessel connection: Ensure the pipe between the system and expansion vessel is not blocked with sludge. If blocked, clean or replace.
• Safety valve: If the pressure relief valve has discharged repeatedly, it may not reseal properly and should be replaced.