I am getting low pressure from my hot water but the combi boiler pressure gauge reads 1.5 bar , what could cause this please ?

The pressure in the boiler is mainly for the heating circuit and generally does not affect the hot water on a combi boiler providing it around 1 to 1.5 bar. A problem I have come across before, which will give the fault you describe, is a partially choked filter in the cold water supply to the boiler ( not the filling loop ). You will need to check with the boilers installation instructions to see if it has a filter and where it is located.

Hope this helps.