You're right on the money here - it was the thermal cutout. Motor
obviously got too hot. So I need to find out what's overheating it.
I've never cleaned the filter - is this the next step? the filter's the
white fabric thing that has a cross shaped plastic holder and fits just
under the motor, above the bag? Can I wash it or should I use some
other kind of liquid. I presume it has to dry pretty well. Where do I
go from here? thanks so far! Andy