The common or garden dryer sheet most of us use in our laundry most of the time, can potentially halve the life of your tumble dryer.
Even if you clean the lint trap filter every load, using those dryer sheets leaves an invisible film on the fine mesh of the filter.
To test whether you have have this problem, remove the filter from the machine and run some water over it. You'd expect the water to pour through, after all it's a clean mesh. If any water puddles remain after this test, you have an invisible build up on your filter which is making the machine work much harder than it should to dry your clothes, potentially cutting the life of the heater unit by 50%.
Fortunately, there is a simple solution. A mix of warm water and soap applied with a soft brush across the surface will easily remove this film. You should repeat this process approximately every six months, depending on how often you use your dryer.