would be looking at the h/e
is the water hot going in
???
I would contact the management and see what they say, try and find the guy that installed it.
This is where the buck gets passed, you contact management and they pass the buck to the heating engineers they say they cannot deal with it as they are heating engineers not plumbers.
Say where you are - one of us might be local.
Im from Walsall (nr bham)
Try looking for a filter in the hose/head. Unscrew head from hose and hose from wall outlet and have a look. If they'd been furtling with the filter in the trevi(mixer) bit that's harder.
When you say the water is ok for a few seconds - pressure/flow OK or temperature ok?
Does it get hotter (eventually) if you turn the tap down and wait?
I dont know where to look for this filter, have no idea where the head or the hose is. As far as im aware the last people that came out were the heating engineers (who were a little annoyed) however they did play witht the filter to the shower.
The water is ok pressure wise although it gets extremely hot before going cool. Ive tried turning the tap down and waiting and it gets luke warm but thats about it!