AO Smith AH-290 Manuel D'installation, Mode D'emploi, Manual D'entretien page 59

Anode:
In order to prevent corrosion of the enamelled hot water tank, the tank is
fitted with a magnesium anode with a ¾" screw plug. This anode has a
life expectancy of 2-5 years. It is nevertheless important to check that the
anode is intact at all times. This should be done by inspecting the anode
every 2 years and replacing it if it is corroded and measures only 6-10 mm
in diameter. To inspect the anode, turn off the power supply to the system
and remove the front cover. The hot water tank has to be drained before the
anode can be unscrewed. To do this, turn off the cold water supply,
attach a hose to the drain valve to ensure the water runs to the nearest
drain. When draining the water from the tank, turn on a hot water tap to
prevent negative pressure in the tank. When the tank is empty, the anode
can be unscrewed and inspected. When the anode has been fitted again,
close the drain cock and turn the valve water supply back on to fill the tank
with water. When the tank is full and the cover back on, the power supply
can be switched on again.
3.3 Demounting / Putting the unit out of service
The following actions must be taken:
Disconnect the power supply from the unit and disconnect other
connections. Shut off the fresh water supply valve and connect a drain
hose to the drain valve in order to drain the water.
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