A vented dryer throws its lint problem outside. A heat-pump dryer cannot: it runs a closed air loop, pulling moist air out of the drum, condensing the water out of it against a cold heat exchanger, reheating it and sending it back. Nothing leaves the machine except the condensate. So every fibre that gets past the door filter stays inside, and where it settles is on the fins of the heat exchanger, which is exactly where airflow matters most.
Asko Prompts for Both
The messages on Asko's Logic-generation dryers are specific, and they are separate for a reason: Clean door filter, Clean the condenser unit, and the combined Please empty the water tank and clean door filter. The fault table adds E4, whose display text is a request to clean the filters or call service, with the action given as cleaning the filters per the cleaning and maintenance chapter. On the older condenser machines the prompts were scheduled rather than measured: Asko's service documentation says Clean condenser is indicated every 100 cycles, or whenever the machine has indicated Clean lint filter twice, and that Clean Lint Filter is indicated when air circulation and temperature are incorrect.
Owners generally do the first one and ignore the second, because the first takes ten seconds and the second involves a panel at floor level.
Before You Open the Lower Access
Switch the dryer off and unplug it, or switch off its breaker. Then leave it. A heat-pump dryer runs a compressor and a refrigerant circuit, and the heat exchanger and the space around it stay warm well after a cycle ends; there is no reason to work in there while it is hot. Once it is cool, put a towel down, because the exchanger holds water and it will run out when the unit is withdrawn.
The Door Filter, Every Cycle
Lift it out and clear the mat of lint. Once every few weeks, run water through the mesh. If the water beads and sits on the surface instead of passing through, there is a film on it, and that film is mostly fabric softener and detergent residue. Scrub it gently with a soft brush, rinse, and dry it completely before it goes back. A wet filter refitted into a dryer is a filter that collects lint into a paste.
The Condenser Unit, Periodically
Work from your own model's cleaning and maintenance chapter, because the retaining arrangement differs between models. Broadly: release the lower cover, unlock the frame or clips that hold the unit, withdraw it squarely, and rinse it in the direction the manual specifies, usually under running water rather than with anything pressurised. Let it drain and dry before refitting, and make sure the cover and any seal go back properly, because a leaking cover lets the machine draw room air into a loop that is supposed to be closed.
Two things not to do: never use a sharp tool, a screwdriver or a stiff wire on the fins, because bent fins block airflow permanently and cannot be straightened out; and never open or interfere with the sealed refrigerant circuit, which is not owner-serviceable at any level.
The Water Tank and the Rest
Empty the condensate tank every cycle unless the machine is plumbed to a drain. Asko lists Please empty the tank before resuming a cycle as one of its ordinary messages. On the older TD60 platform a full tank had its own code, F1, with the action given as emptying the container and restarting the machine. If the tank is being emptied and the machine still reports a problem with condensate, E3 on the Logic generation is a failure of the pump that moves condensate into the tank, and that is a service item.
Also wipe the drum seal and the area around the filter housing, and check the floor vents or the space behind the machine are not blocked by stored items. If drying times have not improved after both filters are genuinely clean, book an Asko dryer repair and say what the condenser looked like when you took it out.