Hi there,
I am new to this site, and new to diy. I have bought a basic shower mixer from wickes at the weekend and fitted it through the taps.
The problem is that I can get hot water as well as cold when the shower head is not on the wall, but as soon as it does go on the wall I can only get cold!
I can get hot water through the taps normally in the bath, and through the showe (although not brilliantly) when it is not up high
The hot water is currrently being heated by the electric rather than the gas to try to save money, will this make a difference?
I am not sure what sort of boiler it is but it is round rather large and is in an airing cupboard in my children's room.

Can you take some pictures with your phone or camera and put them on line so I can see exactly what you have.

The type of fuel for heating makes no difference and I am really thinking hard how a shower head could change the mix. I'll track down a few of the other plumbers and see what comes up, I'm a blank, never heard of this.

Assuming a single handle valve. Valve is probably pressure balanced. Putting shower head on changes pressure. Should be an adjustment ring under handle.

Thank you all for your replies, my partner says that he has adjusted the ring under the handle, that is the first thing as it was on the rong setting , and it is as soon as the cold goes on it cuts out the hot. Unfortunately I am unable to upload any pictures as I have lost my usb cable! Thank you again for all your replies we are just at a loss as to what it is and am dying for a shower!!

Of course I have no idea what this valve looks like. But if you can , try this. Remove the handle or knob, turn the stem 180 degrees and put the handle back on.

Can you give us a brand name for the valve? Regards, tom