Zanussi Washer DryerZ716WT83. Heating problem

The customer reported no drying on the dry cycle. On function test when a drying cycle is selected the program starts water is injected and the pump runs. The fan then rotates and the heater receives a supply for around 15 seconds the it switches off. No error code is displayed. The drying element has good resistance and as the heater receives a supply that circuit would appear serviceable. Is there a sensor that would switch the heater on and off? Any ideas would be appreciated. This machine is three years old but only been in use for the past two weeks. The Zanussi agent came to repair at the machine, looked at and did a runner!!! Didn’t even take the lid off.