On 12/04/2016 08:56, Chris Bartram wrote:

If the pressure is within the acceptable range, then there must be a fault.

It's not just pressure but flow rate that matters. The pressure
might drop too low once the required flow rate is reached.

You need to refer to the manufacturers website and see what
the minimum delivery is per minute. There are special measuring
jugs for this pupose but any graduated container will do.