Zanussi TD 150 won't dry for long?

My Zanussi TD 150 Tumble Dryer keeps cutting out after about 10 mins of drying. It heats up fine, but then cuts out and I have to press the little red button on the top thermostat to get it to dry again.

I thought it was the thermostat so I replaced the one with the red button for a 140 degrees thermostat, but the problem is still there.

Do you think it is the thermostat beneath this one, and if it is this, what one should I get to replace it? I can find ones for 54 degrees and ones for 120 degrees which supposedly fit this tumble dryer. I'm just not sure which one to get.

Any help would be greatly appreciated! Cheers.