Water pressure drop after installing a new shower

Hi,

I've just had my shower replaced with a TRITON T80si electric shower
and just after 2 days the new shower stopped working.
Called in the same plumber who installed the new one and he reckons
our water pressure has gone down.
It seems like a bit of a coincidence to me. Could it have been caused
by the new shower?  Has anyone had a similar problem?

TIA
Prathy