Hot Water Overflow Not Sufficiently Drained
The TPR (temperature pressure relief) or overflow pipe from the hot water system discharges near the building perimeter rather than into a dedicated drain, directing water against the slab edge and creating sustained moisture - a recognised conducive condition for subterranean termites. AS/NZS 3500.4 requires relief valve discharge to be piped to a safe, visible location away from the structure.
Severity rationale
Across 1,045 observations the modal score is 3, with 75% of findings sitting at exactly 3. Score 4 accounts for 4% of cases - typically where the overflow is actively running onto soil against a brick-veneer wall with no gap between the discharge point and the slab edge. The low proportion of 4s reflects that the defect is common but usually correctable without structural work; the risk is primarily from repeated long-term moisture rather than immediate failure. No 5-rated observations were recorded.
Causes
- Overflow pipe cut short at installation, terminating at the base of the hot water unit rather than running to a drain
- No drain point provided near the HWS during original construction, so the pipe discharges to ground
- Pipe extended to the perimeter but directed onto soil or garden bed rather than connected to stormwater or sewer
- Replacement HWS installed without re-routing the discharge pipe to a compliant outlet
- Flexible hose used as a termination point, running water under the slab edge during valve activations
Symptoms to look for
- Overflow pipe visible at the base of the hot water unit, terminating in mulch, soil, or against the slab face
- Water staining, efflorescence, or moss growth on brickwork adjacent to the HWS pad
- Ponding or saturated soil at the building perimeter beneath the hot water unit
- No drain grate or connection point visible near the discharge outlet
- Persistent moisture on the slab edge near the HWS that does not dry between inspections
Remedies
- Engage a licensed plumber to extend the overflow pipe to discharge over a visible drain point, tundish, or sealed sewer connection at least 500mm clear of the building
- Where no existing drain is available, install a small floor waste at the HWS pad and connect the overflow pipe to it
- Re-grade soil immediately around the HWS pad to direct any incidental spillage away from the slab edge
- Inspect the slab edge and adjacent masonry for moisture damage or termite activity once the drainage is rectified
Where we see this most
These suburbs show the highest concentration of hot water overflow not sufficiently drained in our inspection data (minimum five observations). Click a suburb to see its full defect profile.
Worth asking our inspector about this specifically.
Fixing the discharge route is a single plumber visit and prevents sustained moisture at the slab edge. We recommend actioning before the next annual termite inspection so that the perimeter can be assessed under dry conditions.