Boiler pressure rises rapidly when heating and may discharge water from safety valve

Safety: Hot water may discharge from the safety valve. Keep clear of the discharge pipe outlet.

• Check cold pressure: When the system is cold, ensure pressure is not above the recommended value (usually around 1.2 bar). If too high, bleed water from a radiator to reduce it.
• Ensure filling loop is closed: Verify both valves on the filling loop are fully closed and the hose removed if detachable.
• Monitor pressure rise: If pressure still climbs excessively when heating, the expansion vessel likely needs attention.
• Technician tasks: A heating engineer will check the expansion vessel pre-charge, clear any blocked connection, and replace the vessel if the diaphragm has failed.