Where is the water coming from?
| Location | Likely cause | Repairable? |
|---|---|---|
| Relief valve line, occasional drip while heating | Normal thermal expansion | No action usually needed |
| Relief valve line, constant flow | Failed valve or high mains pressure | Yes |
| Pipe connections at the top of the unit | Loose or corroded fitting | Yes |
| Underneath the tank, no obvious fitting | Internal tank corrosion | No — replacement |
| Around an internal unit's tray | Any of the above, plus drain blockage | Depends on source |
Why mains pressure matters
If incoming mains pressure exceeds what the system's valve arrangement is designed for, the relief valve will discharge continually. Fitting or replacing a pressure limiting valve addresses the cause rather than the symptom, and also protects tapware and appliances.
What to do first
- Isolate the cold water supply to the unit, or shut off the water at the meter
- Turn off power at the switchboard for an electric system, or close the gas isolation valve
- Keep the area clear and photograph where the water is appearing
- Call a plumber and describe the exact location of the leak
Never cap or plug a relief valve discharge line. It is a safety device, and blocking it creates a serious hazard.