Almost always because of what stands between that room and the radio: a dense or metal-backed wall, a floor, a chimney breast or a foil-lined insulation board. A stronger router on the same side of the obstacle does not cross it.
The building is the variable, and the specification sheet has nothing to say about your building.
What actually stops the signal
Dense masonry, and especially a chimney breast, a party wall or an internal wall of solid brick or stone.
Anything with metal in it. A metal-framed stud partition, a foil-backed plasterboard, a foil-faced insulation board, a mesh-reinforced screed in a floor, a metal door. These are the ones people never suspect, because from the room they look like ordinary walls.
Water. Pipework, a tank, a large aquarium, and — genuinely — a crowded room, because people are mostly water.
Coated glass. Some energy-efficient glazing has a metallic coating that attenuates radio strongly, which is why a conservatory or an extension can be worse than the garden beyond it.
Distance and floors together. A room diagonally across and one floor up is much further, in radio terms, than its position on a plan suggests.
Why the frequency matters here
The higher the band, the more each of those costs. A wall that a 2.4 GHz signal crosses with a little loss may stop a 6 GHz signal almost completely, and 5 GHz sits between them.
This produces a familiar pattern: the device in the difficult room stays connected on the lower band and is slow, while the same device in the next room is on the higher band and is fast. Nothing is broken — the link has fallen back to what will cross the wall.
What to try, cheapest first
Move the router. Even a metre or two, and especially out of a cupboard or off the floor. The path to the difficult room is what you are trying to shorten or clear.
Change channel. In a block of flats, the 2.4 GHz band is crowded and the three non-overlapping 20 MHz channels are shared with every neighbour. Some units choose automatically and some need telling.
Check for a radio in the way. A microwave oven running in the kitchen between the router and the room is a real and intermittent cause.
What actually solves a stubborn wall
A second radio on the far side of it. There are three ways to put one there.
A wired access point, if a cable can be run — the best answer, because nothing is relayed and the unit is specified in published terms: PoE type, uplink port speed, mounting.
A mesh node, if a cable cannot be run. Place it where it still has a decent link back to the router rather than in the dead room itself, because a node relaying a poor signal serves a poor signal.
A powerline adapter with an access point, where the walls beat radio but the electrical circuit reaches. What it achieves depends on the wiring between the two points, which is not something any specification can tell you in advance.
What is not the cause
The router being old, usually. A newer generation improves how a crowded room is shared and how much a good link carries; it does not change what a wall does to a signal. If one room is bad and the rest of the house is fine, the purchase to consider is a second radio, not a better first one.
The questions that come up before an order
Would a more powerful router fix it?
Rarely, and for two reasons. Transmit power is capped by the regulator, so units are already close to the same ceiling. And the return path matters as much: a phone shouting back at a router across the same wall has a small antenna and a battery, and no amount of power at the router end changes what it can send.
Is the 5 GHz band or the 2.4 GHz band better for a distant room?
For reaching through obstacles, the lower band travels better, which is why it is often the one still connected where the higher one has dropped. It is also the most crowded, so it may be reachable and slow. Where the room can be reached on either, the higher band is generally the better link.
Last reviewed 10 September 2026