There's enough boilers in garages, lofts, the other side of the house, etc, once you overlap it with UK houses being brick, you get enough situations where getting WiFi from one place to another becomes a pain. A lot of the time, the WiFi AP is 30 cm from where the phone line came into the house when it was built (before the internet even existed), which is not optimally placed for coverage.

Fair. But I strongly suspect nearly every house with a garage has the boiler in it.

Edit. So having done a little research this probably isn't the case. Maybe it's a regional thing, all the (mostly suburban) houses I've lived in and visited, in the north west of England, are set up that way.

In the midlands the boiler would preferably be in the utility room (laundry room). The slight waste heat is appreciated there.

In London it's wherever the landlord's plumber can fit it, as he illegally subdivides the house into several flats. At least going by my experience as a student. Kitchen, bathroom, garage, outside wall...