I have mixer tap with a shower attachment in my bath. When you run both hot and cold through the tap it mixes well but when you change it to the shower only hots comes out, even if you turn cold water on more.
I have a combi bolier but I don't understand why the cold water cuts out when it is placed to shower.
check the bath cold water pipe it may have a pressure reducing valve fitted normally with a mixer tap the cold water only needs to be open a very small amount so if you are turning it more than a 1/4 turn it has been governed down to balance it with the hot supply
brian
July 2010
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