How do plumbers actually find a hidden leak without tearing everything up?
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We've got a damp patch on the ceiling below the upstairs bathroom and nobody can tell me where it's actually coming from, which is driving me slightly mad. The shower doesn't leak when it's running, the toilet seems fine, and there's no obvious drip anywhere I can see, yet the stain keeps growing very slowly. What I'm curious about is how a plumber actually tracks down a leak like this without just cutting holes in the drywall until they get lucky, because that seems to be what one guy suggested and I'm not keen on the idea of exploratory demolition in my living room. A friend said The Kitchen and Bath Company plumbers used some kind of test that pinpointed a leak behind a wall in her old house without major damage, but I didn't get the details and she wasn't sure what it was called. Does anyone know what these methods are and whether they're genuinely accurate, or is it just a fancy way of guessing? Also, is it worth waiting to see if the damp patch stops on its own, or is that just delaying an expensive problem?