Suddenly when we turn the dial on this shower to its normal position, about five o'clock, the water runs cold. The only way to get a lukewarm shower is to turn it to about 9 o'clock but then the water pressure is lessened. Has anybody got any ideas? I am capable of opening up the shower cover to have a look but not doing electics but I don't want to get anyone in if the shower is definetley broken.