I really can’t get why people is able to come in for the fist time and ask for help without saying at least “hello/thank you”. Sorry it falls on you, but this is something that really wonders me each time.
That said:
– there is no such thing as “closing sensor”. it’s just a timeout. If the sensor that triggers the doors opening doesn’t detect movement or something in their field, the doors will closed.
– you don’t tell us if the doors close when you help them, which will point a mechanical problem.
– Then if they close, that will be, as already said and by easiest to solve, 1-clean with alcohol and carefully lubricate with silicon. 2-change the belt. 3-Align the doors (search old forum for details).
Hope this helps.