hi I have a myson compact cp53 pump which has started acting up it will now only work on number 3 setting it wont work at all on 1 or 2 is it ok to leave on number 3 as its always been on number 2 for years,, is this a problem with the pump its self or is it with the black electric box on the side with the speed setting if so can this be changed any help advive is much appreciated thankyou.