need to know how overide 824ecto tec plus pressure?

Mine is past the red on the dial..just had the pressure valve changed this morning, but it dropped to virtually nil after an hour..tried re pressurising, but went straight up tp 3.0 bar and can't get it down..still in the red...I appreciate this may now be an expansion vassel prob, but need to know how to reduce current pressure to grey area on the dial please.