Boiler Keeps Losing Pressure? Here Is Why

A combi or system boiler runs a sealed circuit filled with water under pressure, typically around one to one and a half bar when cold. That water goes round and round and nothing should leave. When the gauge falls and the boiler locks out on low pressure, the water has gone somewhere: through a pipe joint under a floor, a radiator valve, a pressure relief valve discharging outside, or a component inside the boiler. Because the circuit is topped up from the mains, the leak can run for months with nothing visible inside the house.

The pattern of the loss tells us a lot. Pressure that drops over weeks is often a weeping radiator valve or a pressure relief valve that has started to pass. Pressure that drops in days points to pipework, and in the 1930s semis around Watford and the Victorian terraces of north and west London that usually means copper heating pipes buried in a solid floor screed or running through a timber sub-floor. In newer houses with underfloor heating the leak is often on one loop under the screed, which is why the floor may feel warmer in one spot.

We isolate the boiler from the pipework and pressure test each part separately, which tells us whether the water is going inside the boiler, at the radiators, or under the floor. On the pipework we use a thermal imaging camera to map the pipe runs while the heating is warm, then hydrogen tracer gas in the drained circuit to pinpoint the exact spot where it escapes through the floor. The leak is marked, photographed and, if you want, repaired through a single small opening, with a written report and the thermal images included.

A leak on a heating pipe under a floor is exactly the kind of hidden escape of water that trace and access cover on buildings insurance is designed for. Our report sets out the tests, the readings and the location so your insurer can act on it without a second visit.