just installed new bath with new mixer shower using existing power pump ,,after 2 weeks ther was no water coming through mixer for shower and the pump did not start , left it for a while then it started ok ,, then it stoped again ,, loosend connector to mixer a little water escaped and the pump started ,, now it has happend again , if I loosen the connector water trickles out and the pump starts again ,,, is the an air lock ,?? any help welcome