Underfloor Heating Leak Detection in Marlborough

Symptoms

The underfloor heating system at a property in SN9 developed a leak that required investigation. On arrival, the UFH circuit had already been isolated, with oil-fired underfloor heating serving the ground floor and radiators running from the same boiler upstairs.

The system was losing pressure, and the source of that loss needed to be traced before any repair could be considered.

This type of underfloor heating leak detection job is complicated by the fact that plastic pipework is buried within a screed or subfloor, making visual inspection alone useless. The leak could have been anywhere along the circuit, and without pinpointing it accurately, any attempt at repair would have meant unnecessary and extensive excavation.

Methods Used

With the UFH circuit isolated, the pipework was disconnected and a compressor was introduced at 2 bar to pressurise the system with air. The pressure dropped immediately — there was no retention whatsoever — and audible air escape was detected through the wall from the test point.

This gave a directional indication of where the leak was occurring, which was then refined using acoustic equipment.

Acoustic detection is well-suited to underfloor heating leak detection precisely because it can identify the leak point without requiring the floor to be broken up across a wide area. By listening along the floor surface, the equipment pinpointed the location to a specific corner of the office room, allowing a targeted and minimal excavation rather than a speculative one.

Investigation Process

1. 1
   System isolated on arrival

   The underfloor heating circuit had been isolated before the engineer arrived. The system was confirmed as an oil-fired boiler supplying UFH on the ground floor and radiators upstairs.

2. 2
   Pipework disconnected and pressurised

   The UFH pipework was disconnected and a compressor was connected, introducing air at 2 bar. The system held no pressure at all.

3. 3
   Audible air escape located through wall

   The sound of air escaping was clearly audible on the other side of the wall from the test point, giving an initial directional indication of the leak area.

4. 4
   Acoustic equipment deployed

   Acoustic detection equipment was used to follow and refine the signal, pinpointing the leak to a specific corner of the office room.

5. 5
   Ground exposed and leak found

   The floor was opened in the identified corner and the leak was found in the 22mm Speedfit PEX pipework buried in the ground.

6. 6
   Temporary repair carried out

   A temporary repair was made to the plastic pipework at the leak point. John Guest do not recommend permanent fittings on this type of buried plastic pipe, so the repair was completed on that basis with the customer's full understanding.

7. 7
   Remainder of pipework replaced in copper

   The section of pipework running back through the wall to the garage was replaced in copper, protected, at the customer's request.

8. 8
   Boiler flow temperature adjusted

   The boiler flow temperature was turned down, and the need for automatic air vents on the high points near the boiler was noted, as the existing vent had been capped off.

Result & Outcome

The leak was located in a corner of the office room, within the 22mm Speedfit PEX pipework buried in the ground. The acoustic approach used during this underfloor heating leak detection job meant that excavation was limited to the specific area where the leak had been confirmed, rather than opening up large sections of floor speculatively.

A temporary repair was carried out at the leak point. John Guest do not recommend permanent push-fit fittings on buried plastic pipework in this application, and the customer was made fully aware that the repair cannot be warranted on that basis. The section of pipework from the repair back through the wall to the garage was replaced in copper at the customer's request, providing a more durable solution for that part of the circuit.

The longer-term recommendation is to re-pipe the flow and return to the manifold in copper, though this would be a significant undertaking. In the meantime, the boiler flow temperature has been reduced to limit stress on the existing plastic pipework. Automatic air vents should also be fitted at the high points near the boiler, as the current vent on the boiler itself has been capped for an unknown reason.