Monsoon Shower pump stuck

Hi

Have a New shower installation
Mira Discovery shower fed by hep Piping
gos via a Monsoon 1.5 Bar Pump located behind shower room at ground level.
Flow is reasonable but more would be good
Problem is the Pump does not run just Buzzes
also it seems that which ever way i move the mixer i only et Hot water
never cold

Ideas ??

Pump blocked/jammed?

On the cold side

How easy is it to open one of those pumps up