We are often asked by clients why hot water occasionally comes out of the cold water tap. It’s usually caused by geysers being installed incorrectly by plumbers and plumbing companies that aren’t registered and have no idea regarding rules and regulations associated with the plumbing industry often causing damage to property and putting lives at risk.

Hot water coming out of a cold tap happens as a result of a geyser being installed or replaced incorrectly. The way the pipework is installed around the geyser and, installing necessary components such as vacuum breakers prevent this occurrence from happening which makes for a safe installation.

The picture below is an example of correctly installed geyser installation in the horizontal position where the cold water supply indicated in blue is piped forming an anti-syphon loop, and vacuum breakers are installed above the inlet pipework as well as above the outlet pipework.

Incorrect installation of a geyser with no anti-syphon loop or vacuum breakers

In the picture below we illustrate the water supply to the geyser without installing an anti-syphon loop or vacuum breakers. The water supply is closed off by the shut-off valve marked “A” that could represent either a plumber or someone turning off the water for an emergency plumbing repair. Alternatively, the council turning off the water to the neighbourhood causing no hot water to flow out the top of the geyser to the hot taps marked “C” and resulting in hot water draining out of the geyser that was supposed to be the cold water supply to the cold taps marked as”B”. There is nothing to prevent the draining of the hot water back into the cold water pipes.

What is the function of the anti-syphon loop?

The anti-syphon loop as illustrated in the picture below is created by piping the inlet pipe to just above the top of the geyser and then piping it back down connecting it to the inlet of the geyser. When a plumber installs an anti-syphon loop to a geyser inlet, it will prevent the hot water from draining out of the geyser when the water supply is turned off as water can’t flow upwards when syphoning occurs. Think of the scenario when you syphon liquidlike petrol out of a container with a hose. As soon as you get the syphon process going by sucking on the end of the hose, you lower the hose for the liquid to syphon out. As soon as you lift the hose above the container, the syphon process stops automatically.

The same occurs with an anti-syphon loop installed on a geyser installation. The hot water inside the geyser can’t drain out into the cold water inlet pipe as it now needs to flow upwards above the water level inside of the cylinder.

What is a vacuum breaker?

A vacuum breaker is a component that is installed on the geyser pipework that prevents water from being syphoned backwards.

How does a vacuum breaker function?

There are two vacuum breakers installed on a geyser installation, one on the hot water outlet side which we will deal with in a separate blog and the other on the cold water inlet side as shown out in the picture above.

The vacuum breaker on the inlet side is installed 300mm above the anti-syphon loop and assists the process created by the anti-syphon loop by opening up a spring loaded seal once a negative pressure is sensed due to water syphoning in the wrong direction. The vacuum breaker will open up letting air into the system breaking the negative pressure which in turn stops the syphoning from happening and prevents hot water coming out of the cold water tap.