Pressure testing: confirming and isolating a leak

How it works

Valves are closed to isolate each circuit: cold water, hot water, secondary return, heating, and each loop of an underfloor heating system from the manifold. Each one is brought to a test pressure and watched for a set time. The circuit that loses pressure is the one that is leaking.

When we use it

• high water consumption with no visible signs;
• a boiler that keeps losing pressure;
• before locating a leak with thermal imaging or tracer gas, to target the right circuit;
• after a repair, to check that the circuit is watertight again.

Limits

A pressure test tells you whether a circuit is leaking, not exactly where. It does not apply to drains, which are not under pressure. A valve that no longer closes properly can skew the result: we take this into account when interpreting it.