Plug oddity

Some plugs are like that, fit a decent plug. If its well tarnished it might be worth scraping the pins clean and trying again.

NT

kgs ago me late mums hoover keymatic washing machine used to do that. Put a new plug on, and eventually a new wall socket as well. Seriously MK both of them before and after.

clean plug and socket and see if it still happens. If the metal isn't too hot to touch that's probably 'not unusual, or a problem'

Of course making sure there aren;t any stray finger paws or feather likely to make contact. if it gets hot, you'd easily be able to see if it's the fuse getting hot, which is what I found once. But tehn again the heater was a ~2.5kw and a 10amp fuse fitted, which was old and tarnished.

Very often the fuse contacts. The fuse can oxidise a bit too. Give it and the contacts a clean and make sure the fuse is a tight fit.

The fuse gives off up to 1W at its current rating. For a 2kW heater on a 13A fuse, this would be (8/13)^2 = 0.4W

Can also be a problem with the pin contacts, and possibly even the terminals in the rear of the socket.

I would recommend you make sure you have a good quality plug and socket where you routinely expect loads of kW's. If the heater is fixed, then an FCU would be better, as that removes some of the possible poor connections points.

(If the heater forms the primary heating for that area, then it should be on a circuit for that purpose, not the ring circuit.)

Turned out to be the fuse holder. I took the fuse out and rotated it in the holder a couple of times. The sides of the holder part for each end of the fuse were almost completely straight, very little bulge to accommodate the curve of the fuse.

Thanks for the various feedbacks.