Candy CIV60 Tumbledryer - Reverse Action not working?

Hi - Recently, after moving my dryer to a different part of the kitchen, it started to only work for a few minutes each time before cutting out and just making a humming noise during the cycle. The filter light was usually (not always), coming on so I took the machine apart as much as I could and cleaned as much fluff as I could from the filter/vents.

Its a bit better now (no light), but still only works for a few minutes, then hums for a few minutes, works again, then hums - I am guessing this means the forward action is working but the reverse isn't? What would cause this?

Thanks in advance