The most important thing to do is stop the flow of water into the tank. Locate the stop tap, normally located where the cold water supply comes into the hot water unit, and turn the water off. If you can't locate the stop tap the next most accessible point will be at the water meter, however this will stop the supply of water to the whole of the residence. It is important to also remember to turn the power off at your switchboard, or gas if applicable.
It is not unusual for the temperature relief valve, located usually at the top of a hot water tank, to discharge water. This can be up to 3 per cent of the tank's capacity every heating cycle. This means that a 250 litre tank can produce up to 7.5 litres per heating cycle that is released from the pressure relief valve.
A steady flow from the pressure relief valve (more than 20 litres a day) may be the result of a faulty valve. Call your plumber for this to be further investigated.
What to Do When You Have No Hot Water
Check for any obvious signs of water leaks. If there are no obvious water leaks this may mean an electrical thermostat is the cause of the problem and requires an electrician. If your water cylinder is a considerable age (more than 10 years) it may be more economical in the long run to replace the unit than repair, especially if signs of corrosion are evident.
What to Do When Your Water is Either Too Hot or Not Hot Enough
The water temperature is controlled by what is known as a tempering valve. If there are no obvious other signs present it may be that this valve needs replacing.
Call your plumber for further investigation.