Internet Slower After Replacing the Router

A common scenario: the provider-supplied router is replaced with a pricier, newer one with more antennas, and the internet feels slower than before. The new router is almost certainly fine. What differs are its defaults, designed to be "safe anywhere", not "fast in your home". These seven settings explain nearly every case, in order of likelihood.

Measure first, over cable

Before changing anything, connect a laptop to the new router with a LAN cable and run a speed test, how to in the speed test guide. If it's full speed, the problem is in Wi-Fi (settings 1–5). If even cable is slow, jump to settings 6–7.

1. Devices are on 2.4 GHz, not 5 GHz

New routers often enable band steering, one name for both bands, and devices that remember that name from the old router land on 2.4 GHz and stay there. Check in the phone/laptop Wi-Fi settings: if it says 2.4 GHz while next to the router, "forget" the network and reconnect. If it's still stubborn, split the band names and join the 5 GHz one.

2. Channel width too narrow or too wide

On 5 GHz, new routers are often set to 20 or 40 MHz "for compatibility". Change it to 80 MHz, that's what makes Wi-Fi 5/6 speed noticeable. Conversely on 2.4 GHz, leave it at 20 MHz; 40 MHz on a crowded band makes things worse. Usually under Wireless → Advanced → Channel Width.

3. Auto channel picked a crowded one

"Auto" on a new router picks a channel at first boot, often at a quiet hour, then sticks with it when the neighbours get busy. Pick a channel manually based on a scan, guide in choosing the right Wi-Fi channel. On 5 GHz, try DFS channels (52–144), usually emptier, if all your devices support them.

4. Legacy compatibility mode is on

Settings like 802.11 b/g/n mixed on 2.4 GHz, or "Legacy mode", slow the whole band for the sake of one old device that may not exist. Choose n only or n/ax on 2.4 GHz and ac/ax on 5 GHz. If a device suddenly can't connect afterwards, that's the old device, give it its own 2.4 GHz mixed-mode SSID rather than sacrificing everything.

5. The new router sits where the old one did

Provider routers often sit with the ONT near where the fibre enters, a corner of the house, near the floor. Even a stronger new router can't push through three walls from a corner. Move it to the centre, table height or higher; the cable from ONT to router can be long. See router placement. And if the antennas adjust, don't leave them all vertical, tilt one.

6. QoS or "protection" features on by default

Some new routers enable QoS, a security scanner, parental controls, or a "traffic analyser" out of the box. These inspect every packet and on mid-range routers can cap throughput at 100–300 Mbps, below your fibre plan. Turn them all off first, measure, then enable only what you actually use, one at a time. For QoS you genuinely need, see the QoS guide.

7. Double NAT: the old router is still a router

The most often missed cause when even cable is slow. If the provider's ONT/modem is still in router mode and the new router is plugged in behind it, two routers are stacked: double NAT, two firewalls, extra latency. The tell: the new router's WAN address starts with 192.168.x.x or 10.x.x.x. Fix one of two ways: ask the provider to set the ONT to bridge mode (new router does PPPoE), or make the new router an access point only. Explained in two routers on one network and the NAT guide.

Last: firmware

A freshly bought router often carries firmware from when it was manufactured, possibly a year ago. The first update frequently improves Wi-Fi performance noticeably. How to in updating firmware; do it before adjusting anything else, so you don't have to redo settings.

Closing notes

Measure over cable first. Slow on Wi-Fi only → 5 GHz band, 80 MHz width, manual channel, legacy mode off, router mid-home. Slow on cable too → disable built-in QoS/security features, then check for double NAT. And update firmware before all of it. A new router doesn't need "time to adapt", it just needs configuring.

Frequently asked questions