Miele ceramic hob F14 Fault ?

Can anyone throw light on this one ?
called out to a Miele Hob yesterday that comes up with a random fault when the fault occurs the touch controls lock up and the hob has to be turned off with the isolater.
the hob is KM 543 EDST/R02, Fabr-nr 5998990 fault display looking from the front is:

F 14 F
E E

the 14 is shown on the clock display front center of hob and
the letters F & E on the hot plate displays.
there appears to be no damage to the control boards and all connections are good the fault seems to rectify itself after about 10mins but occurs again at random any help on this one would be appreciated
Cheers
Auldyn Electrics