The short answer
A Bosch WQB dryer that runs cold is telling you something about its air path or its supply, not usually about its heater. On the three models listed below the heat source sits downstream of a chain of thermal protection, and that chain is designed to open before anything is damaged. The generic advice to test the element first inverts the order that actually finds the fault here.
What you observe on these models
- The drum turns for the whole cycle and the load is still damp — The classic presentation. The machine behaves normally in every other way.
- The load is warm at the start and cold later — A thermal device that opens as things heat up, rather than one that is already open.
- Cycle time runs long or keeps extending — On any machine that senses the load, no heat means the load never dries, so the control keeps going.
- The cabinet and the exhaust are cool to the hand — Worth checking before you open anything, because it separates no-heat from poor-airflow.
Causes, most likely first on the WQB family
- Restricted airflow through the filter and the condenser path — First on the WQB family, and by a wide margin. Fine lint passes the main filter and packs the secondary filter or the condenser fins where it is out of sight, so the owner sees a machine that has been cleaned and still will not heat. If your machine has a lower access door, what is behind it is the first thing to look at.
- Blocked or crushed exhaust ducting — Second where the machine vents outside. A duct that has been shortened, kinked behind the cabinet after a move, or terminated in a flap that no longer opens will produce no heat rather than slow drying, because the protection opens before the load notices.
- Thermal protection that has opened and stayed open — Third: the consequence of the two above. It is a real fault and it does need the part, but replacing it while the restriction remains is the repair that comes back.
Check in this order, and why
- First: clean the filter stack and look for a second one — Ordered first because it is the cause that outranks everything else here, and because a clean-looking main filter tells you nothing about what is behind it.
- Second: follow the duct if the machine has one — Disconnect it at the cabinet and run the machine for a moment. If heat returns with the duct off, the duct is the fault and the machine is fine.
- Third: look for standing lint at the condenser or the lower access door — Where the three models below have an access door low on the front, what is behind it packs with fine lint and is invisible from the drum.
Before you open anything
Safety
Unplug the dryer or switch off its breaker before removing any panel; a capacitor can hold a charge after the power is off. Treat the exhaust path as a fire risk rather than a performance question - lint packed around a heat source is what turns a no-heat call into a fire. If the machine has ever tripped its breaker or smelled hot, stop here and have it looked at rather than running it again to see what happens.
Models in the WQB family
Reference| Model number | Family key |
|---|---|
| WQB235B8AU | bosch:dryer:wqb |
| WQB245AXUC | bosch:dryer:wqb |
| WQB245B0UC | bosch:dryer:wqb |
When to call a technician
The line on the three models below is the first fixed panel. Filters, ducting and the breaker are yours; everything from the thermal chain inwards is a service call, because a cut-out replaced without finding what opened it fails again and the second failure is more expensive than the first. Any smell of burning moves this from a repair to a safety call.
Other faults covered for the WQB family
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
