The fluff filters are clogged.
Clean the fluff filters in accordance with the operating instructions.
The Clean out airways indicator light on the tumble dryer comes on.
Clean the fluff filters in accordance with the operating instructions.
Clean the heat exchanger in accordance with the operating instructions.
Check the heat exchanger at least twice a year – or approximately once every 100 drying cycles in the case of frequent use – and clean it if necessary.