In an earlier contribution to this discussion,
Sadly wrote:


Maybe I will come up with a cunning way to add one of these "1-hour
boost" type switches to my Y-plan system to allow the HW to take
priority for a while - this means that when taking a bath I can hit
the boost so that the hot water takes priority for the next hour...

Maybe I will first get the system working as standard and see how long
it does take to recover!

I have a Y-Plan system with a Danfoss programmer which has a 1-hour boost
facility for the HW. But that just turns the HW on for an hour at a time
when it otherwise wouldn't be on. It doesn't turn CH off for that period.

It seems to me that you either need a very fast recovery cylinder and a HW
priority facility OR a method of allowing the HW to get hot while the CH is
on without interfering unduly with the CH. I have a balancing gate valve on
my HW circuit which can restrict the flow a bit so as not to interfere with
the CH. Obviously the water would take a bit longer to heat when this was
partially closed. This is not a problem unless you want a lot of baths in
quick succession.

My current modus operandi doesn't use the gate valve, but runs the HW and CH
asynchronously. I use the main programmer to time the HW, and a programmable
room stat to time the CH - so that they can be on at non-overlapping times.
This means that the gate valve can be fully open - allowing the water to
heat up as fast as its (non fast-recovery) heat exchanger allows. Admittedly
it doesn't cater explicitly for unscheduled hot water demands - but has
never caused any problems that I am aware of.
--
Cheers,
Set Square
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