In an earlier contribution to this discussion,
John Rumm wrote:

wrote:

It's not really that many drops entering the system over a period of
time more that the pressure in the two systems will try to equate
over a period of time. If the mains is the same pressure as the
"sealed"

Unlikely I would ahve thought. Most combis will have the blow off
valve set at between 3 and 3.5 bar. Mains water will frequently be
more than that.


"Try to equate" is correct. It will take a long time at a very small flow
rate, and the safety valve will operate before it actually gets there. From
what the OP said, it was getting that way before he decided to do something
about it!
--
Cheers,
Roger
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