Internal Cold Mains Leak Detection in Cricklade

Symptoms

At a property in SN5, the customer had turned off the stopcock after noticing the sound of running water coming from an external utility room. There was also visible puddling outside the utility room, and the customer reported they had not needed to top up the heating system in recent weeks.

These signs pointed to a cold mains leak somewhere between the external entry point and the internal pipework.

The combination of audible water noise at the point where the hot and cold supplies entered the utility room, along with the external puddling, indicated a breach in the buried pipework. An internal leak detection assessment was needed to establish the exact location and extent of the leak before any remedial work could be planned.

The situation was further complicated by the condition of the pipework itself. The 15mm copper pipe had no protection against acid erosion, making it susceptible to pinhole failures — and, as the investigation would reveal, this was not an isolated problem confined to a single point in the pipe.

Methods Used

The investigation began with pressure testing to determine which section of pipework was compromised. The internal cold mains failed a 4.5 bar test within 5 minutes, while the external cold mains held pressure over a 20-minute test at the same pressure, narrowing the fault to the internal section near the utility room entry point.

Tracer gas was then introduced, with bubbling confirming the leak at the exact point where the hot and cold supplies entered the external utility room. Excavation at that point revealed a pinhole in the 15mm cold supply pipe, which was repaired — but a further pressure test then identified a second leak on the same pipe, further along beneath the concrete slab.

Given the unprotected, substandard condition of the pipework and the risk of further failures, it was agreed with the customer to isolate and cap both supplies rather than attempt another in-slab repair. As is standard practice in internal leak detection, an endoscope camera was used inside the kitchen to trace where the supplies branched off to serve the utility room.

This led to the discovery of the tee-off point beneath a carousel unit, which required dismantling and partial floor cutting to access before the pipes could be capped.

Investigation Process

1. 1
   Arrival and initial observation

   On arrival, a noise of running water was audible at the point where the hot and cold supplies entered the external utility room, and puddling was visible outside. The customer confirmed the stopcock had already been turned off.

2. 2
   Internal cold mains pressure test

   A pressure test was carried out on the internal cold mains at 4.5 bar for 5 minutes. The test failed, confirming a leak on the internal section of the cold supply.

3. 3
   External cold mains pressure test

   A separate pressure test on the external cold mains at 4.5 bar for 20 minutes passed, ruling out the external pipework and focusing attention on the internal supply into the utility room.

4. 4
   Tracer gas investigation

   Tracer gas was introduced into the pipework. Bubbling occurred at the point of entry of the hot and cold supplies to the external utility room, pinpointing the leak location.

5. 5
   Excavation and first repair

   Excavation at the tracer gas location revealed a pinhole in the 15mm cold supply pipe. A repair was carried out using two 15mm push fit couplings and a short length of copper pipe.

6. 6
   Further pressure test reveals second leak

   A follow-up pressure test after the first repair revealed a further leak on the same pipe, located below the repair point within the concrete slab.

7. 7
   Decision to isolate and cap supplies

   The condition of the unprotected pipework — with no defence against acid erosion — was discussed with the customer. It was agreed to isolate and cap off both the hot and cold supplies to the utility room to prevent further failures.

8. 8
   Endoscope investigation in kitchen

   An endoscope camera was used in the kitchen to establish where the supplies were teed off to feed the external utility room, identifying the branch point beneath a carousel unit.

9. 9
   Access to tee-off point

   Kick boards were removed and the carousel unit dismantled. A multi-tool was used to cut away the unit floor to gain access to the pipes below.

10. 10
    Capping and final pressure test

    Both the hot and cold supplies to the external utility room were capped using two 15mm push fit cap ends. A final pressure test for 15 minutes passed, confirming the system was sound.

11. 11
    Drying recommendation

    Dehumidifiers were recommended to dry the affected area fully before any reinstatement work is carried out.

Result & Outcome

The leak was located in the 15mm cold supply pipe at the point where the hot and cold mains enter the external utility room — confirmed by tracer gas and physical excavation, which revealed a pinhole failure in unprotected copper pipe. A first repair was completed on site, but a subsequent pressure test identified a second fault on the same pipe further along beneath the concrete slab, consistent with the pipe's unprotected and deteriorated condition.

Rather than carry out a further in-slab repair on pipework with no acid erosion protection — which would leave the risk of ongoing failures — it was agreed with the customer to isolate and cap both supplies to the utility room permanently. As part of this internal leak detection process, an endoscope camera traced the supply route through the kitchen, and the tee-off point was accessed by dismantling a carousel unit and cutting through the unit floor. Both pipes were capped at that point.

The final 15-minute pressure test passed, confirming the system is now secure. The utility room supplies are permanently isolated, removing the ongoing risk of further in-slab leaks from the same degraded pipework. Dehumidifiers should be used to dry the excavated and affected areas before any reinstatement takes place.