High system pressure fault, pressure gauge near or above 3 bar, safety valve may discharge water

Safety: Hot water under pressure can cause burns. Allow the system to cool before relieving pressure.

• Check filling loop: Ensure both valves on the filling loop are fully closed and the flexible hose is removed if required by local code.
• Relieve excess pressure: When cool, bleed water from a radiator or drain point until the pressure drops to around 1.5 bar.
• Observe pressure changes: If pressure rises rapidly again during heating, the expansion vessel may be faulty or uncharged.
• Expansion vessel check (technician): A professional can isolate and test the Viessmann expansion vessel pre-charge with a gauge and recharge or replace it if the diaphragm has failed.
• Do not cap safety valve: Never block or cap the pressure relief valve discharge pipe. If it drips continuously, it may need replacement.