A red LOS light is indicating that there is no light coming to the ONT or it is faulty. All you can do is check that the green plug is correctly plugged into its socket. Do not look down the fibre, the light is invisable and will damage your eyes.
If the fiber is plugged in correctly the LOS light should go out and the PON light will be solid green.
If those basic checks don't help you will need to contact Sky who will get Openreach back.
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I remember the Internet starting!
Sky Full Fibre & Virgin Media XGS-PON, with automatic failover using DrayTek multi WAN router.
Sky Q, which will be sadly missed when they decide to kill it off!
