Device for heating the bacterial proliferation zone of a water heater to prevent legionellosis

An electric water heater comprising a cylindrical tank having a vertical wall and an inwardly curved bottom, said bottom defining with said wall an annular, stagnant water zone susceptible of bacterial contamination, said tank being provided with a cold water inlet conduit opening into said tank close to the bottom thereof, a hot water outlet conduit on top of said tank, an upper immersion heating element controlled by a first thermostat and a lower immersion heating element controlled by a second thermostat, said lower heating element being located above said annular zone of contamination,

• wherein the tank further comprises at least one additional outer heating element mounted on said tank vertical wall, outwardly thereof and at the level of said annular zone of contamination below said lower immersion element, said outer heating element being activable to bring water in said annular zone of contamination to a temperature sufficient to eliminate the danger of such bacterial contamination, and
• wherein said first and second thermostats are adjusted so as to operate according to the following priorities:
• said upper immersion heating element is activated first;
• and said bottom immersion heating element and said outer heating element are activated subsequently.