Thanks all for you advice, someone who has fitted a few has also
advised me to suck on the shower head as the has had to do that many
times to get them working initially. If I can get it going, I will
make sure there is no insulation under the unit and try to construct
something around it also to protect it come winter.

Ironically the water pressure with the old pump broken was fine and I
was not sure weather to bypass the bump and just use flow under
gravity but tho id go this way just to have a more powerful shower.
Wish id gone the other way now.