There are three main models of hot water units, and with each the most common cause of hot water loss is corroded tanks or baffles. The life expectancy of hot water unit tanks varies however in normal conditions this occurs around ten to twelve years after the initial unit was fitted. In most cases the unit will require all or part of the unit to be replaced.
Storage Hot Water Units
Gas storage units have a pilot flame continuously burning and with the use of a thermostat to ignite an element and heat the water in a storage tank above.
In certain extreme weather conditions the pilot flame can blow out, if you are to re-ignite the unit follow the instructions carefully (these instructions are often on the back of the small removable panel at the bottom of the unit) and make sure you keep all body parts and your face away from the access penetration.