ACV
Overpressure / Safety Valve Discharge
Water heater leaking from safety valve discharge pipe
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Failed ACV expansion vessel (loss of air charge), Faulty pressure reducing valve on cold supply, Limescale preventing safety valve from sealing, System pressure set too high
How to Fix / Troubleshooting
Safety: Discharged water may be very hot. Keep clear of the discharge outlet.
- 1. Check pressure: Read the pressure gauge on the ACV heater. If pressure rises significantly when heating, suspect expansion issues.
- 2. Test expansion vessel: Isolate and drain pressure from the system. Measure the air charge at the vessel Schrader valve. Recharge to the value specified by ACV (often around 3 bar for potable side, but check manual) or replace the vessel if the diaphragm has failed.
- 3. Inspect safety valve: Briefly operate the test lever to flush debris. If the valve continues to drip afterwards, replace the ACV safety valve.
- 4. Check inlet pressure: Measure cold mains pressure. If above the rating of the heater, install or replace a pressure reducing valve.
Persistent discharge indicates a serious pressure control problem and must be corrected to avoid tank damage.
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Repair Difficulty
Medium
3/5
Required Part
Safety Valve / Expansion Vessel
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