Cutting out is usually a sign of low water pressure. Check the following;
-Kinks in lance hose or water feed hose
-Are you running a very long water feed for the hose (you can get pressure drops at longer runs of 75ft+)
-Is the water pressure low? Is there a washing machine on when you are...
You will always need to secure the water hose with a jubilee clip to prevent it popping off. Also when you fire up the washer hold the trigger on to take the pressure off the pump as it kicks into life.