On Tue, 16 Nov 2004 08:02:03 -0600, (m Ransley)
wrote:

If you loose the air bubble and have to drain something is wrong with
your system and it will not have expansion capabilities and can
overpressure. Water in it when cold - tank is to small, or it does not
drain properly- blockage, or bad autrotrol valve, or bad auto feed, over
filling system. Pressure - altitude gauge may be bad if you rely on
that for monitoring and manualy feed. Often pressure relief will
release on even a partialy full tank from overpressure on a fully hot
boiler, your relief valve could be bad also. Maintain overpressure and
boilers do not last. Start with a new presure gauge and set boiler to
right level.


The expansion tanks most likely to leak air are those with a glass
tube level indicator. The service tech is supposed to open the hand
valves, check the level, then close the hand valves. If the hand
valves are left open, air will eventually escape past the upper glass
tube gasket. Seems like I have to close hand valves everywhere I go,
because the guy who was there before me left them open.

Gary R. Lloyd CMS
HVACR Troubleshooting Books/Software
http://www.techmethod.com