The red LED is an overheating indicator. If the hub is in a hot or poorly located situation, then the solution is to move it somewhere more open, turn it off, restart and hope the red LED has cleared. This can work, and if it does, problem solved.
If that isn't the case, then because this is undoubtedly driven by a sensor on the CPU within the hub, it means that either that the overheating sensor is faulty, or the CPU is indeed overheating. In either case the hub needs replacing because it isn't viable to undertake the complex task of fault finding and replacing solid state components soldered intro low value consumer goods.
If it CPU overheating, a probable cause is dislodgement, delamination or poor initial fitting of the heat sink, and the consequence of an overheating CPU is usuallynot a fire risk, because the CPU will usually be designed to throttle down performance, which would make it operate less reliably. For some light use that might not show, but it would still be happening. If the CPU doesn't throttle back, and the heat sink isn't doing what it is supposed to, its temperature can rise to levels that would damage the silicon, and couldbe a fire risk.
So there's no circumstances that you or any VM customer should tolerate a hub 3 displaying a red LED, any more than you'd tolerate your garage insisting that the tyre pressure warning light showing on your car was nothing to worry about. And if VM still insist that it is nothing to worry about, you should consider contacting your local trading standards, the Office for Product Safety & Standards, and the Consumer's Association if you're a member.
In mostcases, you wouldn't be able to tell if the hub was overheating from the outside - the issue here is that the board or CPU is getting hot because the heat it routinely generates isn't being properly dissipated by the heat sink. So unless it actually did catch fire (again, a low risk, but still a risk) the heat output and surface temperature will remain normal for the Hub 3, that seems to be around 37-39 C.
Whilst I don't KNOW this for a fact, it seems to me from the VM language that customers are reporting here that VM have run out of new hubs because of incompetence in their planning of their supply chain, although unsurprisingly they're entirely able to find sufficient new hubs for new customers. So in addition to skip-diving to salvage and re-issue six year old post-use relics in the form of the old Superhub 2ac, there is every appearance that staff have been told to tell existing customers with Hub 3's showing red LEDs that these are not in fact any form of problem at all. The decent, safety-first practice would be to stop signing up new customers until they can secure a supply of new hubs, and use the ones they do have to resolve existing potential safety problems. Whilst the fire risk from any hub is very low, I will point out for the benefit of VM's lacklustre management that the Grenfell Tower fire is believed to have started in a Hotpoint fridge-freezer with a known problem in the wiring that created the risk of overheating, but which an investigation advised customers to continue using because it was deemed "low risk".
I'll flag this for staff to advise, they'll probably want to send a technician out, if the hub is not replaced then report back here, with details of all interactions when VM staff have stated that the hub can be safely used with an overheating indicator showing.
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