Here’s a quick tip regarding something which could create a fault on a modern tumble dryer. Modern tumble dryers usually use sensors to detect the dampness of laundry inside the drum. Lime in our water or cleaning agents can form a barely visible lining on the inside of the drum, which can interfere with the readings. The result could be that laundry can still be a little damp after drying.
I’ve no idea how common a problem this is, and other faults can cause the same symptoms, but if your dryer appears to be working ok except it’s just leaving clothes a little damper than it used to do it’s worth thinking about this issue. If you suspect you could have a problem, use a vinegar-based cleaning product to wipe all around the inside of the drum and its paddles.