I have the same problem with Stoves 720EF. I ignored for months, as only occasionally happens, but now tripping every time power turned on to cooker. Opened cooker and found that cooling fan is point at which power spike on fan control pcb output during on/off is leaking to earthed cooker chassis (as no problem when cooling fan is run when not screwed to chassis). Tried replacement fan timer pcb (part 082814400 from gdhaonline.co.uk £22.16) but no improvement. Will try replacing fan next - but haven't seen exact type online.
Andy
October 2010