Probably the water flow cannot be switched off completely and the stop valve has to be repared. Apply the eye-shower a cupple of times and check if the valve stops the water flow properly. If not ask for repair. You cannot repair this problem yourself.
If the eye-shower is OK you should remove all lime. Yes: Concentrated hydrochloric acid works fast and pretty good, but the eye shower will be damaged afterwards. Use diluted citric acid instead, have a lot of patience and be busy with a brush!