Found the answer, simple really, disconnect all water connections, and turn pump upside down, if pump kicks in fine, if not pump is useless. Only let pump run for a second, otherwise you will risk damaging the pump.
Just swopped out a burnt out watermill shower pump, professionally fitted about 3 years ago, for a Salamander CT50+.
Basically a like for like replacement.
New pump will not run.
Power to pump OK
Good water flow under gravity to shower head (aprox 6lts/min).
How can I prove if it’s a faulty...