electric boiler problems

[cgh31]

this may make me sound a bit stupid but here goes! I have an electric boiler that seems to have stopped working recently. When I flick the switch on the socket I can hear a hissing noise but the water does not heat up. Does this mean the filament has broken? Can the filament but replaced on its own or will I need a whole new boiler. How much money am I looking at and who do you get - a plumber or an elecrtician? Thanks in advance.