siemens tumble dryer

we have multiple faults on a siemens wt46e389gb/15 tumble dryer. on extra dry it completes program and dries the clothes. on cupboard dry it runs for about 10 mins and beeps to say its finished but the clothes are still hot and wet. if i run the cupboard dry prog on low heat it works ok. on some other progs it only runs for about 10 mins and flashes f09 error. ive checked the overheat resettable stat and that is ok. anyone have any ideas what this could be? I can see a temperature limiter or thermistor next to the overheat stat and i was wondering if this could create these faults if it is failing.
Thanks mark