Quick answer
A warm patch on a tiled or concrete floor is a slab leak on the hot-water line, almost always the buried geyser supply. Cold-line leaks present as cool, damp spots instead. Because the pipe is under the slab, the water has nowhere to go but sideways and downwards, so foundations and screed take the damage long before you see water. This one does not wait.
Common causes
- Corroded hot-water copper running under the slab
- Failed under-slab joint, often at a change of direction
- Pipe laid in direct contact with concrete without sleeving, abrading over time
- Excessive mains pressure accelerating failure at a weak point
- Movement in the slab stressing a rigid buried pipe
What you can do now
- 1Mark the warm area with masking tape and photograph it with a thermometer reading
- 2Check the water meter with everything closed to confirm an active leak
- 3Switch the geyser off for a few hours and see whether the warmth fades, which confirms the hot line
- 4Note whether adjacent grout lines are darker, indicating moisture rising through the screed
- 5Avoid laying rugs over it — you want to keep watching how far it spreads
When to call a professional
Book within days. Slab leaks undermine screed and foundations, and a hot-water slab leak also runs your geyser continuously. Detection will pinpoint the run so the repair can be a targeted break-out, or so the line can be re-routed above ground instead — often the better long-term answer on an older property where the rest of the buried pipe is the same age.
Typical cost in Johannesburg
Detection R950–R1,800 · Re-route R3,500–R8,500
Indicative ranges only. We provide written, itemised quotes before any work.
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