UPDATE:   December 24, 2010
 Winter solstice tree shading and expansion tank failure

The winter solstice is approaching and I started to notice a performance
drop-off in the solar gain in the storage tank.  More than could be expected
due to the diminished solar hours.  Also one of the pumps was running
slower and quieter than I expected in the middle of the day.  I eventually traced
 this down to a shading issue on the solar panels that power the pumps.

So I took the lowest 20 Watt panel and moved it higher.  I also plan to
talk with my neighbor about topping the pine tree involved since
it's not going to stop growing.  I actually had to trim another tree
on our side of the property line a few years back.

A month or so ago the pressure tank had failed which caused very
high pressure in the storage tank.  The first time I dealt with excess
pressure in the system, I had installed an undersized pressure tank by
mistake.  My solution at the time was to
install a pressure gauge/switch
that activated the floor circulation pumps so that heat could be dumped
to the radiant concrete floor.  So this system was still in place to protect
my system from over-pressure.  I think the bladder in the tank failed
due to trapped air and excess heat, these tanks should be installed
BELOW the pipe rather than above as I have done, but I did not have
anywhere else practical to install it.  I decided to try a different style
tank made by Heliodyne:

The original Amtrol Extrol tank uses a diaphragm across the whole tank:

The Heliodyne that I replaced it with uses a balloon style pressure bladder:

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