Fibre internet problems: fix the common ones yourself before you log a fault
Most business fibre issues are local and quick to fix: a router that needs a reboot, weak WiFi, or a wired test you have not tried yet. Work through the cheap checks first, learn to tell your network apart from the line, and only call the ISP when it is genuinely theirs to fix.
How do I fix common fibre internet problems at my business?
Start with the cheapest checks: reboot the router and ONT, plug a laptop in with a cable to rule out WiFi, and test the speed wired. Check the ONT lights to see if the line itself is down. Most faults are inside your own network. Only log a fault with your ISP once you have confirmed the line, not your kit, is the problem.
Start here: is it your network or the line?
Almost every fibre complaint splits into two categories. Knowing which one you are in saves an hour on hold.
Layer one is your own network: the router, WiFi, cabling and the devices in the office. Layer two is the fibre line itself, from the ONT on your wall back to the provider. The fastest way to tell them apart is a wired test. Plug a laptop directly into the router with a network cable and run a speed test. If the wired connection is fine, the problem is your WiFi or a device, not the line. If the wired connection is also broken, check the ONT lights next.
Where the fault usually sits
Five quick checks before you call anyone
Run these in order. They cost nothing and clear the majority of faults in a few minutes.
Seven common fibre faults and how to fix them
Match your symptom to the table, then apply the fix. Most sit firmly in your own network.
| Symptom | Most likely cause | First fix |
|---|---|---|
| Slow speeds | WiFi congestion or a capped line | Test wired; check your plan speed |
| Connection drops | Router overheating or firmware | Reboot; update firmware; ventilate |
| No connection at all | Line fault or power loss | Check ONT LOS light; reboot |
| Poor WiFi coverage | Distance, walls, interference | Reposition router; add a mesh node |
| High latency or ping | Congestion or a far-off route | Test wired; prioritise key traffic |
| Fibre cable damage | Physical break outside | Log a fault; this one is the ISP’s |
| Frequent slowdowns at peak | Shared capacity or too many devices | Check device count; ask about capacity |
Before you spend an hour on hold, plug in a cable. If the wired connection is fine, the line is fine, and the fix is yours to make.
WhichVoIP editorial view
When it really is your ISP, and what to have ready
Some faults are genuinely the provider’s. Recognise them, then log the fault with the right detail so it gets fixed once.
It is the ISP’s problem when the ONT shows a red LOS light, when a wired test is also broken, when an area outage is confirmed, or when speeds stay far below your plan on a wired connection after a reboot. When you log it, have your account number, the ONT light status, your wired speed-test result and the times the fault occurs. For a business line, ask what the service-level agreement promises on restoration time, and whether a failover option such as an LTE backup is available so a single line outage does not stop you trading.
Our verdict
Most fibre problems a business hits are local and fixable in minutes: reboot, test wired, sort out WiFi placement, and read the ONT lights. The skill is not deep networking, it is knowing the order to check things in and how to tell your kit apart from the line. Do that, and you will resolve the common faults yourself and log the real ones with enough detail to get them fixed fast.
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Frequently asked questions
Why is my fibre slow even though I pay for a fast plan?
What do the lights on my fibre ONT mean?
How do I know if the problem is my router or the fibre line?
My fibre keeps dropping. What should I check first?
Should my business have a backup for fibre outages?
When should I call my ISP instead of troubleshooting myself?
Keep reading
Sources: WhichVoIP editorial troubleshooting guidance; standard fibre ONT indicators (power, PON, LOS) and wired-test diagnostics. Provider-agnostic, no brand-specific claims. Verified 25 June 2026.