The short answer
A Bosch WTW-series dryer that tumbles without drying is usually short of airflow rather than short of heat, because a ventless condensing dryer depends on a loop that a restriction closes long before anything electrical fails. this designation denotes the heat-pump condensing platform, and the tell is at the end of a cycle: the load comes out barely warm and the cycle runs long, because the machine dries below the temperature a heating element works at.
What you observe
- The load comes out cold and damp — No usable heat reaching the drum, whatever the panel says.
- The load is warm but never dries — Heat is present; the moisture has nowhere to go.
- Cycles have been creeping longer for weeks — A restriction building gradually rather than a part failing suddenly.
- NEAR MISS - the load is dry but only lukewarm to the hand — On a heat-pump machine that is the design rather than a fault: it dries below the temperature an element works at, and a cool dry load is a working machine.
Likeliest causes here
- The heat exchanger or condenser block packed — The second stage of the loop collects what gets past the filter, and a packed exchanger stops the machine condensing at all. First on this family, and for a reason that belongs to the platform: on this platform the exchanger is where the heat is actually made useful, so it leads.
- The lint filter blinded — Lint you can see is not the problem; the softener film you cannot see is, and it closes the mesh to air while looking clean. Second here, and close enough behind the first to be checked in the same pass: it is first because it is free, instant and right more often than anything else.
- The refrigerant circuit and its compressor — On a heat-pump machine the circuit is the heat source, and a circuit that has lost charge tumbles cold. Ranked third on these models: licensed work, and the least likely of the list.
- A thermal cut-out that has opened — Restrict the air and the machine gets hot where it should not; the cut-out opens and the heat stops, which is the protection working. Last, and the ranking is the point: it is a symptom of a restriction rather than a fault on its own, which is why it is never fixed alone.
- Where this ranking departs from the brand-generic page — The cause that moves is the heat exchanger or condenser block packed. It leads on this family because the heat here comes from a refrigerant circuit rather than from an element. That is a property of the platform rather than of the brand, which is why the page above this one cannot rank it the same way.
Check in this order
- Open the lower flap and clean the exchanger properly — Follow the plate on the flap. This is the single highest-value check on this platform and it needs no tools.
- Run a hot tap through the lint filter — Water should pass straight through the mesh. Beading water is a blinded filter, and that alone stops a load drying.
- Feel the cabinet at the base during a long cycle — A circuit doing nothing leaves a machine that stays cool everywhere, and that goes to a technician.
- Note whether heat stops part way rather than never starting — Heat that dies mid-cycle is protection tripping, and the restriction that tripped it is the real fault.
Before you open anything
Safety
Unplug the appliance or switch off its breaker before removing any panel - a capacitor can hold a charge after the power is off, and the heating side of a dryer holds more stored energy than most of the cabinet. Let it cool before opening the lower flap.
When to call
The filter, the exchanger behind the lower flap, the tank, the room and the load are owner ground on these models, and on this platform they explain most no-heat calls outright. The line is the heat source: a clean machine that still tumbles cold needs a meter, and that means the cabinet open.
Nearest pages
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
