Just sorted the same prob. Pull dryer out to gain access to rear, start drum rotating, set to low/high heat, feel on curved metal cover on back, if hot, heater elements/thermostat ok.
My fault cleared by cleaning out the air flow filter on front of dryer.Pull down 'flap' door at front, unclip 3 x retaining clips, pull out filter, check inside-can be viewed from top. To clean properly, undo 2 x small screws on left/right side, ease out unit with small screwdriver and the use similar to clear out all fluff and gubbins, which prevent correct air flow.
I cleared pens tops, a tennis ball sized wedge of wet fluff and various coins!
Cost of heater unit-£35-54. Cost of a clear out £0!
Good Luck.
P.S. Obviously always clear the filter inside door betwen loads!
R J Pocock., August 2008