The source I suspect is age - it's a 20 year old Panasonic - and it's more a case of 'when' we replace it rather than resolve but an opinion of the source of the problem would be interesting.
About once every 2 months recently it has stopped working properly and requires to be switch off at the wall for an extended period (in the order of an hour). Once it was the touch pad that misbehaved and three times there's been no or little microwave power. It works perfectly well after this full re-boot.
Any ideas ? Thanks Rob