Underfloor Heating Leak Detection in Battle

Symptoms

A property in TN31 was experiencing a concealed leak somewhere within its extensive underfloor pipe network. The property has underfloor heating throughout, set beneath tiles in screed, with additional pipework running inside a large channel under a plastic membrane — a configuration that makes pinpointing any leak particularly difficult.

A drainage system under the property meant that leaking water was draining away rather than pooling visibly indoors, instead surfacing outside through the brickwork as a constant drip.

Methods Used

Given the complexity of the installation — underfloor heating beneath screed, a membrane layer, and a buried pipe channel running across multiple rooms — a systematic multi-method approach was required. Underfloor heating leak detection in a property like this demands careful elimination of each possible source before any access is made, so pressure testing was used to narrow the fault to the hot supply before any physical investigation began.

Damp readings, thermal imaging, acoustic listening, endoscopic camera inspection, and dye testing were all deployed in sequence to build a complete picture of where the water was going and where it was coming from.

Investigation Process

1. 1
   Initial observations

   The water meter at the front of the property was observed moving at approximately two-minute intervals with no water in use, and a constant drip was visible coming through the brickwork outside — both consistent with a pressurised leak draining through the sub-floor drainage system.

2. 2
   Damp meter survey

   Damp readings were taken across the boiler room floor and along the water-damaged plasterboard wall, confirming elevated moisture throughout the area where the pipework runs.

3. 3
   Pressure testing all supplies

   Pressure tests were carried out to all water supplies. Pressure held on every line except the hot supply, which showed a clear drop, identifying the hot supply as the source of the leak.

4. 4
   Thermal imaging of underfloor pipework

   The thermal camera was used to map the underfloor heating circuits in the screed, distinguishing them from the hot and cold supply pipes running in the channel beneath the membrane.

5. 5
   Endoscopic camera inspection

   The endoscope camera was inserted through a gap at the end of the pipe channel in the front room, visually confirming the sub-floor area was very wet and that water was spreading along the channel in both directions.

6. 6
   Acoustic listening and wall access

   A leak noise was detected behind the plasterboard wall in the boiler room using acoustic listening equipment. With the customer's permission, access was made through the wall, revealing a large volume of water on the concrete floor beneath and the leak visibly escaping from a 22mm/22mm/15mm T-piece fitting on the hot supply.

7. 7
   Fitting replaced and pressure re-tested

   The faulty T-piece fitting was removed and replaced with a new Hep20 22mm/22mm/15mm T. A further pressure test confirmed the system was holding with no further active leaks.

8. 8
   Dye testing of waste pipes

   Dye was introduced into the waste pipes running under the property to rule out any contribution from that system; no dye was traced, confirming the waste pipes were sound.

Result & Outcome

The leak was located behind the plasterboard wall in the boiler room, on the hot water supply. It was found to be coming from a 22mm/22mm/15mm T-piece fitting within the buried pipe channel beneath the property. The fitting was removed and replaced with a new Hep20 equivalent on the same visit, and a pressure test carried out immediately afterwards confirmed the system was holding with no further active leaks present.