Internal Cold Mains Leak Detection in Mablethorpe

Symptoms

The owner of a detached property in LN12 had no visible signs of a leak anywhere in the building — no damp patches, no wet walls, no obvious damage — yet water was being lost at a rate of approximately 20 litres per hour. The combi boiler was holding pressure normally, and there was nothing at the upstairs bathroom, downstairs shower room, or either WC to suggest where the water was going.

Because the loss was hidden and the customer had no indication of where to look, an internal leak detection survey was the appropriate course of action. Jobs like this, where there is measurable water loss but no visible trace, typically require a systematic approach to isolate sections of pipework before deploying specialist detection equipment.

It was also noted that the same area of the property had suffered a leak eight years earlier, though the customer was not aware this was relevant to the current situation.

Methods Used

The investigation began at the external meter to establish whether the leak was internal to the property or on the supply upstream. Once confirmed as internal, pressure testing with a rig attached to the outside tap was used to isolate the cold feed to the boiler — ruling it out — before identifying the leak as being on a hot pipe.

Tracer gas was then introduced into the pipework, and thermal imaging was used alongside acoustic equipment to narrow down the location before any floor was broken up.

This staged approach is standard practice in internal leak detection: eliminate sections of the system methodically, then concentrate detection effort only where the evidence points. By the time the floor was opened, the leak location had already been confirmed to a precise area in the rear hallway, minimising unnecessary excavation.

Investigation Process

1. 1
   External meter checked

   The external meter was observed with the internal stopcock open and then closed. Movement was visible when the stopcock was open and stopped when it was closed, confirming the leak was internal from the stopcock onwards.

2. 2
   Pressure rig connected to outside tap

   A pressure rig was added to the outside tap to allow controlled isolation and pressure monitoring of sections of the internal pipework.

3. 3
   Cold feed to boiler isolated

   The cold feed to the boiler was isolated and the pressure gauge showed no drop, ruling out the cold supply as the source of the leak.

4. 4
   Hot pipe identified as source

   With the cold feed to the boiler reopened, pressure began to drop on the gauge, confirming the leak was on the hot pipework.

5. 5
   Tracer gas introduced

   Tracer gas was added to the pipework and was detected coming up through the floor in the rear of the hallway — the same area where a leak had occurred eight years previously.

6. 6
   Acoustic equipment used to pinpoint

   Acoustic detection equipment was used to narrow down the exact position of the leak within the area identified by the tracer gas.

7. 7
   Floor broken up and leak found

   With the customer's permission, the floor was opened in the rear hallway and the leak was found on a 15mm hot pipe feeding the basin in the downstairs WC.

8. 8
   Pipe repaired and system tested

   A small section of 15mm copper pipe and fittings were used to repair the leak. The system was tested, no further leaks were found, and no movement was visible on the external meter with everything reinstated.

Result & Outcome

The leak was found on a 15mm hot pipe beneath the floor in the rear hallway, feeding the basin in the downstairs WC. The location was consistent with a previous leak in the same area eight years earlier. A small section of copper pipe and fittings were used to carry out the repair on the same visit, and testing confirmed no further leaks were present anywhere on the system.

The precision achieved through internal leak detection — working from meter confirmation through pressure isolation, tracer gas, and acoustics — meant the floor opening was targeted and limited to the area where the leak had already been confirmed. There was no exploratory breaking up of multiple areas.

The exposed area will need time to dry out before pipes are covered, the floor is re-screeded, and tiles are reinstated. The customer has been advised to involve their insurer to assess the reinstatement work required.