I have a sealed central heating system. I keep topping the system up but the
pressure always drops. There is one radiator that always is hot at the
bottom and cool at the top, i bleed the rad and then eventually it returns
to previous state. Any ideas ?
Probably Ed Sirett's faq cover the answer, but I had a similar loss of
problem, and it turned out the air expansion vessel ( which has a rubber
diaphragm in it )
had lost its integrity. The result was that there was no expansion space in
and when the CH water was heated, it expanded, elevated the system pressure
( as there was no expansion space ), and blew CH water out of the
valve ( tripped at 2.4 bar ). I never saw it happen as I was ever outside to
watch when this
must have been happening.
The cure, if that really is your problem, is to recharge the
expansion vessel via the
top-up valve on it, and see if the problem recurrs ( may be necessary to
week or two if it's a slow leak ). If it does, the vessel diaphragm may be
leaking and you'll need a new one.
A neat trick to use to find whether your expansion valve is blowing, is to
but a balloon (or condom if inclined) over the valve outlet. Obviously, the
balloon inflates with water or is blown off if the valve engages ;-)
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