I had this problem with my first dryer (tumbled OK but no heating). In desperation, after basic checking I bought another used dryer of the same model which ran for over a year OK until it recently developed an identical problem. A local electrical handyman checked the usual heater assembly, trip switch and temperature probe and all were found to be OK. He then took the circuit board assembly away to check the micro-relay block on the board (the large cream coloured block that the main heating selector switch goes into) and found the contacts inside were scorched and pitted. Replaced that component with a new one (for a couple of £££ from his electrical parts "supplier"). That restored the heating function perfectly. Total cost to me was £47 (which included his call-out fee). As I had saved the circuit board assy from my FIRST dryer, I'm now confident that this will also have the same component failure. So, after the electrical micro-switch has been replaced, this circuit board can then be used as a backup in the event that my current dryer ever exhibits the same fault again in the future.
I would suggest that rather than fork out for a new machine if yours fails in the same way, that you might first consider having this component replaced first (if possible) rather than purchasing the whole circuit board assembly (which varies between about £249 to over £300 on ebay or from Bosch replacement parts websites. I hope this helps.
Clive in Scotland, May 2017
