A geyser failure is one of the most expensive plumbing problems a household faces, because the damage is rarely limited to the unit itself. Ceilings, cupboards and flooring take the cost.
Watch for water that runs hot and then cools quickly. This often points to a failing element or a thermostat that no longer holds its setting.
Listen for knocking or rumbling when the unit heats. Sediment build-up in the tank traps water underneath and boils it, which stresses the tank wall.
Check the overflow pipe outside. A constant drip is not normal and usually means the pressure control valve is passing.
Look at the drip tray and the ceiling below it for staining. A slow leak leaves a mark long before it becomes a burst.
Rusty water from the hot tap only, discoloured and metallic, suggests internal corrosion. At that point replacement is safer than repair.
A geyser that trips the electrical board is a fault, not an inconvenience. Switch it off and book an inspection.