We have a bath/shower mixer, one where the handset rests on a cradle. over the past month, when having a shower the temperature has been too hot to bear. it appears as if more hot water than cold is getting to the shower head. When on the bath filling setting, the cold water easily overpowers the hot when the taps are fully opened. is this likely to be a fault with the mixer itself or could there be a problem elsewhere?.any ideas how i could check or remedy this fault/ Thanks