The Netgear switch did hang when the temperature got excessive.

The symptom was that the even numbered ports just "froze" with the activity lights permanently on.

I got a uprated fan kit and fitted that and the problem went away. Even in the hottest day of the year a week or so ago, all the kit in the loft was fine.

However, when I bought the televes Avant 5's, two of them failed soon after where the power led started flashing.

Googling for common faults revealed that a single 16uF electrolytic cap was prone to drying out and going high ESR and they were rated to 85 Deg C within the power supply section.

So I got a pack of Panasonic FM series 105 degree extra low ESR capacitors and replaced the problem prone capacitor on all 4 televes avants.

Not had any more problems since.