We had a series of light switches replaced by an electrician about 18 months ago. Over the past few weeks three of the upstairs switches have failed ie they no longer turn the light on. This was usually preceeded by a short period of the switches working irregularly or the lights occasionally flickering when on. So is it normal for three new-ish switches to fail so soon? Or is there something else wrong? Many thanks (before I call the electrician)