non working tap

Hi, a monobloc tap is indeed removed from under the sink either by unscrewing a very large plastic or brass nut or by unscrewing a 13 mm ish nut off a central long stud which releases a horseshoe shaped retaining plate, removing a sink is a doddle, nothing to it, it just depends how its held, either by screws on show on top of the sink or by clamping plates under the sink, usually at the corners.
But you may be able to get to the tap without removing the sink if you are lucky.
What you do from the top of the tap is get to the micro switch, then further down the mixer insert, first as you have done, remove the retaining screw under the hot/cold indicator button, then lift off the handle, then unscrew the top 1 inch of the body, it is sometimes quite hard to get it to turn, when done, or if it hasn't got one, you should be seeing a micro switch surrounded by a brass nut about 30mm wide, to remove this you usually have to use long nose pliers, lift the microswitch off its holder then remove the nut, you can then remove the insert for replacement, if its the microswitch at fault the best thing to do is cut off the cables, solder them onto the new ones then from underneath pull them through, cut off the excess & fix them to the originals.
Keith...P.S.
Who is this idiot posting these adverts