At 02:32 PM 8/31/2009, Rocket J Squirrel wrote...
>Or put a teaspoon of salt into the tank each time I fill it. This is
>easier. I'll do that next time and see if it works. Pity about adding
>salt
>to such clean water, tho'.

Have you tried simply shorting the common (lowest level) contact to
each of the other ones to see what happens? It can be done on the
outside of the tank. If there's a break in the common circuit, that
could explain the problem.