totally wrong putting cold mains gravity pumped hot
you need balanced pressures to have a proper shower install you should of used a twin pump.
depending on the pump ie salamander recommend 600mm between showerhead and base of cws tank.
pos/neg head pumps are all for gravity setups but you must do the install as they state or you'll get problems
and your warranty will be void.
hi-spec plumbing & heating (essex), March 2010