"Christian McArdle" wrote in message
et...
The thought has just occurred to me that with 2 pumps, and the boiler
interlock logic implemented using relays, he may not need *any* zone
valves - and almost certainly wouldn't need any by-passes. He'd just have
to
make sure that the HW circuit didn't continue to circulate by gravity when
CH-only was demanding heat. This might require a null-flow valve on the
cylinder side of the vent/feed connection.

Christian.


I read the postings with interest, and gain a lot of knowledge on the
way.....

I assume that the two pump option is similar in operation to the the
grundfos pump plan which uses a dual output pump.

What puzzles me on this is if, say the HW circuit was being pumped by its
own pump and CH was off, why there would be no circulation on the CH circuit
without the a zone valve? i.e wouldnt the HW pump push water through the
pump and around the CH circuit? (on the current gravity system, isnt the HW
assisted to a degree by the pump when CH is on, as we are pushing pumped
water into the boiler return)