Water heating – water dripping from pressure relief valve drain vent pipe

Cause

Hot water cylinder temperature is set too high

Repair

  • water in a storage cylinder must be heated to over 60°C at least once a day to prevent the growth of Legionella bacteria. Water temperatures higher than this, however, can lead to risks of water from taps being dangerously hot and/or a waste of energy

  • check that the thermostat is set to 60°C. Reduce to this temperature of it is set higher

  • if dripping persists, call a licensed plumber

Cause

Faulty pressure relief valve – it is not shutting off under working pressure

Repair

  • every hot water cylinder requires a method of pressure relief because water expands with heat, increasing pressure. Occasional dripping is not a cause for concern – it just shows the system is working. If you turn off the power supply to the cylinder for 10–15 minutes and the dripping stops, then what you have is normal expansion of hot water

  • if dripping is continuous and excessive then there is a problem. Gently open the test lever to allow a discharge of water and any gritty material or minerals that may be contributing to the problem

  • if water doesn’t come out of the tank during this test, call a licensed plumber immediately

  • if water comes out during the test but dripping continues, the valve may be faulty or worn out and requires replacement. This is not a task that a homeowner can carry out – call in a licensed plumber. You can check whether someone is licensed here

Cause

Build-up of lime preventing the pressure relief valve from shutting off fully

Repair

  • flush the valve using the test lever as described in the repair above

  • if this does not work, call in a licensed plumber

  • valve manufacturers typically suggest that homeowners operate the test lever once a year

Cause

Increase in water temperature where a solar panel is connected

Repair

  • see the first repair above

  • solar water heating systems are often proprietary systems. Call the installer or manufacturer for advice