Pressure Testing and Pipe Tracing

A house has several separate pipe systems, and only one of them is usually leaking. The cold mains feeds the taps and the cistern, and the hot water comes from a cylinder or a combination boiler. The central heating is a sealed loop of its own, and underfloor heating runs as several loops off a manifold. A leak shows up as a damp patch or a falling gauge without saying which of these it belongs to. Searching all of them at once is slow. Isolating each one and testing it under pressure narrows the search to a single system within the first part of the survey.

For a pressure test the system is drained or isolated and charged with nitrogen to a set pressure, then watched on a gauge. A system that holds pressure is not leaking. One that falls is, and the rate of fall gives a rough idea of the size of the escape. For heating we connect gauges at the boiler and at a radiator so a drop can be seen across the whole circuit, and underfloor loops are tested one at a time at the manifold. Nitrogen is inert and dry, so testing adds no water to a floor that is already wet.

Pipe tracing here means mapping where the pipes go, not electronic cable tracing. Plans are rarely accurate and pipes are routed around obstacles by whoever fitted them. With the heating running, the thermal camera picks out warm pipes under floors and behind plaster, and a run of cold mains shows as a cold line on a warm floor. Where the camera cannot see, a borescope through a small existing gap shows the pipe in the void. The result is a marked route on the floor or wall, so that when something has to be opened it is opened in the right place and nowhere else.