the light is saying low water pressure to the shower ,how is the water supply to other taps? may need to open incoming stop tap some more, funny things happen when workmen mess around with the water mains and don't note how many turns valve was open.
On the other hand if a mains repair was done near to you rubbish could have been admitted to the water main supply pipe and it could now be in your shower supply pipe.
NOTE.
the water company will deny this has happened or could happen.
wirecutterman, November 2009
