A friend's combi-driven CH system is losing pressure. After refilling, the pressure drops to zero within two hours. No obvious leaks upstairs, downstairs or in the unheated cellar where the downstairs pipes are visible.
He thinks it must be leaking under the relatively recent concrete-floored extension.
Is that a reasonable conclusion?
If so, how can the leak be pinpointed? He's hopeless at DIY and I'm at the other end of the country but in general terms, is there a way to prevent the entire floor being dug up in the search?
He's had a plumber in who pumped in some leak sealer to no effect.
What should he do next?
And can anyone recommend a reliable plumber in E17 / Walthamstow? (He's away for Xmas anyway so he's not requiring an emergency call out on Xmas eve.)
Thanks for any pointers.