Internal Cold Mains Leak Detection in Wandsworth

Symptoms

The garden room and gym at a property in SW19 had suffered severe water damage, with walls and flooring saturated throughout the space and its integral bathroom. The extent of the damage was significant enough to warrant a full trace and access investigation to identify the source before any remedial works could be considered.

Because the damage was widespread and not confined to a single visible point, internal leak detection was necessary to distinguish between a pressurised supply failure and other potential causes, including possible roof ingress affecting the high-level areas of the bathroom. Both the mains and hot water supplies serving the garden room required systematic testing to isolate which — if either — was responsible.

The customer was advised that all trace and access works would fall under their buildings insurance policy, and that a full report would be required to support any subsequent insurance claim.

Methods Used

The investigation began with a visual inspection of all affected areas, followed by damp meter testing across walls and floors to quantify the saturation. Both the mains and hot water supplies were isolated at the kitchen of the main house, then subjected to individual pressure tests using compressed air at 4.0 bar over one hour each.

This allowed the engineer to confirm which supply was leaking before introducing tracer gas.

For an internal leak detection job of this complexity — with damage spread across multiple rooms and no obvious point of failure — tracer gas was the method needed to pinpoint the exact location. Once gas was introduced to the confirmed leaking supply, the engineer methodically traced the route until a concentration was detected at a specific boxed section adjacent to the WC.

After the repair, a final pressure test confirmed the supply was holding. A separate observation was made regarding high-level damp in the bathroom, which was identified as potentially unrelated to the supply failure and referred for further investigation through insurance.

Investigation Process

1. 1
   Visual Inspection on Arrival

   The engineer carried out a full visual inspection of the garden room, gym, and integral bathroom, finding severe leak damage with walls and flooring saturated throughout all areas.

2. 2
   Damp Meter Testing

   Damp meter readings were taken across all affected surfaces, returning maximum readings throughout every area tested.

3. 3
   Supplies Isolated at Kitchen

   Both the mains and hot water supplies serving the garden room were isolated at the kitchen of the main house to allow independent pressure testing of each.

4. 4
   Hot Supply Pressure Test

   4.0 bar of compressed air was added to the hot supply and held for one hour with no drop in pressure recorded, confirming the hot supply was intact.

5. 5
   Mains Supply Pressure Test

   4.0 bar of compressed air was added to the mains supply and held for one hour, during which a gradual pressure drop confirmed a fault on this supply.

6. 6
   Tracer Gas Introduced to Mains Supply

   Tracer gas was connected to the mains supply and charged to 4.0 bar; a gradual pressure drop continued, confirming an active leak on the mains.

7. 7
   Leak Located Behind Boxing at WC

   Gas traces were detected escaping from within a boxed section to the left of the WC; the boxing was removed to reveal a failed 15mm pushfit elbow as the source of the leak.

8. 8
   Repair Carried Out

   The failed 15mm pushfit elbow on the mains supply was replaced, restoring the supply.

9. 9
   Post-Repair Pressure Test

   4.0 bar of tracer gas was re-applied to the mains supply for one hour with no drop in pressure recorded, confirming the repair was successful and the supply was holding.

10. 10
    Further Visual Inspection — High-Level Bathroom Damp

    A secondary visual inspection identified high-level damp and damage in the bathroom consistent with a potential roof issue; this was flagged as a separate matter requiring further investigation through insurance.

11. 11
    Customer Advised on Insurance

    The customer was informed that the trace and access works are covered under their buildings insurance policy and advised to submit the engineer's report to their insurer to proceed with all remedial and drying works.

Result & Outcome

The leak was traced to a failed 15mm pushfit elbow on the mains supply, located behind boxing to the left-hand side of the WC within the integral bathroom. Removal of the boxing confirmed the fitting had failed and had been saturating all surrounding areas. The elbow was replaced, and a post-repair pressure test held 4.0 bar for one hour with no drop, confirming the mains supply was fully restored.

For an internal leak detection case like this, where damage is extensive and spread across multiple rooms, establishing exactly which supply is at fault before introducing tracer gas is essential — the pressure testing on the hot supply ruled it out entirely and directed the investigation to the mains. The precise location identified by the tracer gas meant access was targeted to a single boxed section rather than requiring widespread opening up of the structure.

Separately, high-level damp observed in the bathroom is considered likely to have a different origin, possibly roof-related, and will need independent investigation. The customer has been advised to forward the full report to their insurance company, with all trace and access costs covered under their buildings insurance policy.