How do you find a water leak inside a wall?

The hard part of a leak inside a wall is that the water rarely appears where the pipe has failed. It runs along a joist, drops down a cavity and shows up in the next room, or a floor below, several feet from the actual fault. That's why cutting into the plaster at the wet patch so often finds nothing but wet plaster.

In an older Macclesfield house this gets harder rather than easier, and it's worth knowing why before someone starts opening things up. The Victorian terraces and stone cottages have solid walls, not cavities — so pipework was chased into the masonry, or clipped to the face and plastered over, and damp spreads through solid brick and stone in ways it never does through a cavity. Add a century of alterations, a chimney breast that has been blocked up, and floorboards that have been lifted by six different trades, and the wet patch on the wall tells you very little on its own.

This is what leak detection equipment is for. A thermal camera shows the temperature difference where water is tracking. An acoustic detector picks up the sound of water escaping under pressure, even through a wall. A moisture meter maps how far the damp actually extends. Between them, you get a hole in the right place instead of three in the wrong ones.

If your home insurance includes "trace and access" cover, this is exactly what it's for — it's the part of the policy that pays for finding the leak and opening up to reach it, separately from repairing the damage. Worth checking your policy before anyone starts cutting.