When the LOS light turns red or blinks red, it usually means your ONT or fiber router is not receiving the optical signal properly from the network. When it's green and steady, everything is fine. However, when it blinks red or stays solid red, it signifies a Loss of Signal, a problem preventing your router from communicating. If you find that the Optical/Config/PON Light on your Fibre ONT (Optical Network Terminal) box is flashing, has gone off, or has gone red, this indicates there may be an issue with the fibre connection coming into your property. What Can I Do? First, please check that the optical cable which comes. The PON light on my Openreach ONT is solid red, which I understand indicates a loss of fibre signal. You'll need a tech out to get it fixed, unfortunately. Nope, only fix is to switch ISP's. This guide explains the likely causes, the checks you can do at home, and when the issue needs technician support.
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