On Sun, 08 Apr 2012 09:59:15 -0700, wrote:

Here's an interesting question. If you had a second water heater in
parallel that was 6 years old and not being used, would you turn it off
but leave it full. Or drain it? Any guess as to which would result in
longer life so that it could then be used when the active one fails?

I was wondering something similar.

I've had things turned off that never went back on again (due to crud, I
guess). Once I left a perfectly well running car outside for six months,
and it was a bear to get it going again.

I realize the dynamics are different ... but do people actually turn off
hot water heaters for long periods of time (like years) and then turn
them back on again.