Salamander CT75 not turning on with Mixer turned on

[wobbler64]

Hello and Help !
I have connected to my shower a Salamander CT75 Pump.
It is located down beside the hot water tank. The hot water connection is 15mm less than 2m in distance.
The cold connection comes from the cold water tank.
The shower head is below the cold water tank by approx 2 ft.

Problem:
When I turn on the mixer in the shower nothing happens.
Until I pull out either outlet fixing (hot or cold, it does not matter) to let some water out, and reseat fitting the Salamander CT75 kicks into life.

fyi
With pump powered off,when I turn on the mixer - nothing.
I put a NVR on the cold water outlet thinking it might be air bubble, but no difference

Thanks for any advise, i'm now stuck.
Bill

 

[Balenza]

Have you got at least 1 litre/min per side (hot or cold) natural flow at the shower head ?.