Eusebius wrote:
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?

Yes, the motor in a Henry is a direct cooled one. In other words the air
being sucked in is blown out over the motor to keep it cool. If the filter
is clogged the airflow drops, so the cooling effect is reduced.

The white nylon type filter can be cleaned, scrub it with a brush & some
detergent, but make sure it's bone dry before its used again - or replace
it.

Dave