The message
from Martin Rich contains these words:

When this happened before (around 3 years ago - the machine is about 7
years old) we called the service engineer, who I'm sure just pulled
the machine out and pressed a reset button. Searching through the
archive of this group, I found references to some Bosch driers having
a red reset button on the back, but I can't see such a button on ours.
I wondered if anybody with knowledge and experience of this particular
model knew where it might be?

It may not be red! Look for a things like a large washer with a bump in
the middle, or just about anything that looks like a button - or even
not much like a button at all, and push it. Hard.

--
Skipweasel
Pay no attention to that man behind the curtain.