If your pal has the manual or instruction booklet for the taps,
then ask him / her to check and see if it is for a high pressure
system.

Occasionally, taps can be converted by removing a flow restrictor on the
inlet pipework. If there is one on the hot inlet, take it out! They often
take the form of a plastic screw inserted into the pipe that seriously
reduces the available bore.

The other possibility is that there is an airlock in the pipe to the tap.
This frequently happens in gravity systems where there isn't the pressure
and flow to blast air pockets out along the pipe. These can often be
resolved by connecting the mains cold to the gravity hot for a short time to
blast the air pocket back into the cylinder where it vents off. This is
easily done at a mixer tap by sealing up the spout with some sort of rubber
or squashy plastic pad held on with a tea towel and turning on both taps.
Don't do it too long, or you'll water spouting out of the vent and
overflowing the header tank.

Christian.