How do I fix my zanussi TC7103W?

I have a zanussi tumble dryer model TC7103W it stopped heating so I fitted a brand new heater element it worked for less than 24 hours now it wont stay on it still works but goe's out after 30 seconds or so so can't dry any clothes, I checked the thermostat I have continuity with my multitester so Iam baffled why the heater element wont stay on.

Regards Tony Wilkins