if a relay had gone I would expect the element to glow all the time unless the unit is turned off but can be certain
if you leave the unit will it ever stop heating ?
don’t know the unit but normally there is an indication on the display that it has either got to temp of it is getting hot. have you got any indications of this type ?
bear in mind this unit is over 10 years old and if the board is faulty its likely it come un-programmed making it a manufacturer only repair
dave