Plumber doesn't reply back after leaving us with a botched job

[king of pipes]

I've looked through some of my photos from past installs these help you understand better how a shower pump should be installed the hot water supply to the pump needs to be via a Essex flange fitted in the top of the cylinder this avoids air entering the shower pump the cold supply is taken from the cold water storage tank to the cold side of the pump. Kop

 

[king of pipes]

Surrey flange can also be used

 

[Ric2013]

...and there are other acceptable methods. The point is there must be a dedicated and air free source of water for the pump, usually in 22mm pipework.