Jinx wrote:
> The element in our hot water cylinder failed yesterday (didn't quite
> make its 19th birthday) and an electrician came today to replace it
> 
> 
> This must be long-standing corrosion and it absolutely amazes me
> that it has taken until now to pop the circuit breaker. Surely the
> winding must have been wet before yesterday. 

Maybe not.  My limited understanding is that water heaters use a 
sacrificial anode that has a lower potential than the rest of the 
heater.  It slowly corrodes away during the life of the system.  When 
it's gone, corrosion continues with whatever material has the next 
higher potential.  This rapidly destroys the heater at that point.

Water heaters are sold with particular lifetimes - eg, 15 year, 20 year, 
etc.  Same heaters, different longevity.  How?  Longer sacrificial 
anode.  An electrician told me to buy the shorter lifetime heater at a 
lower price and replace the anode with a 30 year one.
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