slow delivery?

What could be wrong air or wrong pump.
Truma Ultraflow pumping system submersible pump external barrel.
Changed pump because the existing problematic, stopping and starting and not delivering any water.
Connected the replaced pump now hear water entering slow delivery at mixer tap in kitchen sink. Both hot and cold slow delivery.
Basin taps in toilet and shower head also slow. May have been some air in system but still slow so is it possible all air not expelled? I ensured the pump polarity was correct as this is a symptom of reversed polarity although work deliver slow.
Pressure switch seems to work clicks and the panel control pump switch light goes off.
Turn on tap after ten seconds light comes on pump activates again slow delivery then after 18 sec light goes off.
Now wondering if there are two types of submersibles one for electric toilet the other for fresh water, giving different deliver y rates per min. The pump I put on to replace the original carver one has no name or flow delivery details. Unfortunately package it came in gone.
Many thanks