Not drying correctly AEG Lavatherm 37320 Electronic vented tumble dryer?

Machine operation seems normal but not drying correctly even after long period of operation.
It has good warm airflow through vent pipe. Filter and vent line clean and clear with good vent airflow.
Checked heating element is okay for continuity,
Wiring seems ok.
Main thermal heat switch on top of heat box is not open circuit allowing elements to heat.
If machine is started with no wet washing in the drum it heats quickly and shuts down after approx 30 seconds.
When started with damp towels in drum operation seems normal warm air etc but takes too long to dry.
Suspect maybe a 'stat' problem not allowing full heating but not sure best test method to check stats for correct operation.
Am qualified electrician but without circuit diagram for this appliance.
Grateful for any advice from engineer who may have experienced on this type of AEG tumbledryer
machine is in remote location so not easy to send to service centre.
Please advise,