Yeah, it's a condensing drier, so all the dust gets merrily circulated round the internal ducting. The lint filters that they install don't seem very effective, since even larger bits of fluff and hair make it past. I cleaned everything out already, including the heating element, which only had two wisps of fluff in it. There was a thin layer of fine dust on many of the surfaces, but nothing that could cause a blockage or even significantly restrict flow.
The problem didn't occur with the lid off the drier and it pulled out from the wall, which was more evidence for it being a temperature related issue. I'll probably reconnect the board next but leave it hanging out the front of the machine, cover the gap with something to keep the heat in, and then retest. If the fault occurs with the board out, then it can't be anything to do with the board overheating.