Do I need to change shower isolation switch?

Having just gone from a 7kw shower to an 8.5kw electric shower, it worked for 10 minutes before the isolation switch light went off, the pull cord seized and the shower went cold. I have no idea what the ampage of the present pull cord switch is as it was fitted with the 7kw shower. Do I need to buy a new pull cord isolation switch at 45amp in order for the shower to work?