The municipal ripple relay is off. You can confirmed by checking if the switch is in the off position on the relay box. If this is the cause, you will need to call the Eskom faults line. For more info please visit Eskoms website or contact them directly
It may be that electrical wires are melted or not making proper contact. A registered plumber will need to re-wire the electrics on the geyser.
The geyser isolator is faulty. This requires the isolator switch to be replaced.
The thermostat may not be working. The thermostat may need to be changed.
There may be an element burn out. May require installation of a new element by a registered plumber.
There may be a leak in the hot water pipe. If you are unable to see a leak, then a leak detection by a registered plumber is necessary.
The shut off valve to the geyser is off. Simply turn the valve on.
The pressure valve is blocked or clogged. The pressure control valve needs to be removed and cleaned. If you are unfamiliar to do this yourself, then contact your local registered plumber.
The tap washer or cartridge is stuck. If this is the case, change the washer or cartridge.