Hot Water Overflow – Hot water Cylinders Electric/Gas/Boiler systems

If you have a hot water overflow this is usually caused by one of two things. There may be a pressure issue which will mean your hot water cylinder system valves may need replacing or servicing. The second cause may be normal thermal expansion which is caused by the element heating up and the volume of the water inside the cylinder expanding, which causes overflow water to vent onto the roof, or out of the wall via the overflow pipe (depending on which hot water cylinder system you have).

If there is also steam, with a hot water overflow then that can be a sign that the thermostat is not working correctly, and the cylinder has overheated, which will require the thermostat to be tested, and likely replaced.
To test whether a hot water overflow is normal thermal expansion or a pressure issue, turn off the power to your hot water cylinder, for 10 minutes and see if the overflow stops.
If the overflow stops then the hot water overflow you have seen is perfectly normal. However, if the hot water overflow does not fully stop, that will be a pressure issue, and you need the services of a plumber – call Bennett Plumbing and Drainage.

When you call, please be able to advise which hot water cylinder you have – check the label on the side of your hot water cylinder, to advise if it is a mains pressure or low-pressure cylinder.