Concealed Cold Mains Leak Detection in Bath

Symptoms

At a property in BS31, the customer noticed water damage to the kitchen wall and had lifted some of the vinyl floor tiles in the kitchen to investigate. The heating and hot water were supplied by a combination boiler, and the customer had not needed to top up the heating system in recent weeks, suggesting the issue was isolated to the cold water supply rather than the heating circuit.

The visible signs pointed to a leak somewhere beneath or within the kitchen, but the exact source and route of the pipework were unknown. A water mains leak detection survey was required to locate the fault without unnecessary disruption to the property.

Methods Used

The investigation began with pressure testing to isolate which section of the cold mains was at fault. The internal cold mains held pressure at 4 bar for 20 minutes, passing without issue.

The external cold mains failed a 4-bar pressure test within 5 minutes, confirming the leak was on that section of pipework. Damp meter readings were taken across the kitchen and returned elevated readings on both sides, consistent with water tracking through the floor and wall.

Tracer gas was then introduced into the pipework. High gas readings were detected behind the dishwasher and within the internal kitchen wall, giving two precise points of interest.

This combination of pressure testing, damp readings, and tracer gas is the standard methodology for water mains leak detection of this type — it narrows the fault zone before any excavation begins, minimising unnecessary disruption. Acoustic listening was also used during excavations to confirm activity at both locations before cutting was carried out.

Investigation Process

1. 1
   Initial assessment

   The customer had already lifted some vinyl floor tiles in the kitchen. Water damage to the kitchen wall was noted, and the heating system was confirmed not to have required topping up, pointing away from the heating circuit.

2. 2
   Internal cold mains pressure test

   The internal cold mains were pressure tested at 4 bar for 20 minutes. The test passed, ruling out the internal section as the source of the leak.

3. 3
   External cold mains pressure test

   The external cold mains were pressure tested at 4 bar for 5 minutes. The test failed, confirming the leak was on the external cold mains supply.

4. 4
   Damp meter survey

   Damp readings were taken on both sides of the kitchen. High readings were recorded on both sides, indicating moisture had spread across the floor area.

5. 5
   Tracer gas investigation

   Tracer gas was introduced into the pipework. High readings were detected behind the dishwasher and in the internal kitchen wall, identifying two specific locations for investigation.

6. 6
   Dishwasher removed, first excavation

   The built-in dishwasher was removed to allow access. Excavation behind the dishwasher revealed the 15mm incoming cold mains encased in Armaflex lagging.

7. 7
   Second excavation at internal wall

   Further excavation was carried out in the concrete screed floor at the location of the high tracer gas reading near the internal wall. Acoustic noise was confirmed at both excavation points.

8. 8
   Pipe cut and extracted

   Following discussion with the customer, the 15mm copper cold mains were cut at both excavation points. The pipe, approximately 3 metres in length, was pulled out and a leaking soldered joint was found — identified as the cause of the leak.

9. 9
   Repair carried out

   The leaking copper pipe was replaced with approximately 3 metres of 15mm Hep20 pipe, using one straight coupling and one 15-degree elbow.

10. 10
    Post-repair pressure test

    The external cold mains were pressure tested at 4 bar for 30 minutes following the repair. The test passed, confirming the repair was successful.

11. 11
    Dishwasher refitted

    The built-in dishwasher was refitted following completion of the repair and pressure test.

Result & Outcome

The leak was traced to a faulty soldered joint on the 15mm copper cold mains running beneath the kitchen floor, approximately 3 metres in length. The pipe was encased in Armaflex lagging and routed under the concrete screed, making it inaccessible without targeted excavation at two precise points identified by tracer gas and acoustic listening.

The leaking copper pipe was removed in full and replaced with 15mm Hep20 using a straight coupling and a 15-degree elbow. A post-repair pressure test at 4 bar held for 30 minutes without any drop, confirming the repair was sound. The dishwasher was refitted on completion.

For a water mains leak detection job of this type — where the leak is concealed within a concrete screed floor and behind fitted kitchen units — the targeted approach avoided large-scale disruption. The recommendation now is to dry out the affected area thoroughly using a dehumidifier before making good the floor and carrying out any redecorating.