"John Rumm" wrote in message
...
Dave wrote:

Given that the bypass will usually only come into play when the pump
is on overrun and there is no call for heat from any stat, so the
boiler will be off. So who cares?



Or when most of the TRVs are off but the stat is calling for heat?

Yes precisely. So Drivel's argument that "By-pass valves defeat the
purpose of a condensing boiler" is nonsense. As you say, the only time
it will be passing water (assuming its correctly adjusted) are in
situations where there is no alternative flow path and the boiler ought
not be firing anyway.

Total tripe. All TVRs could be down and only the downstairs toilet slightly
open. A call for heat. The by-pass will still open as the flow through the
rad will not be enough for 90% of boilers. Many rads may be calling for
heat and the by-pass can still be open. Then the spring wears in time,
making it open even more. They are a waste of time and should be avoided.
Makers put them on boilers in order to protect themselves from idiots. It
is easy to design them out.



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