In an earlier contribution to this discussion,
TheScullster wrote:

Hi all

Does anyone have a link to a comparison of these systems.
Struggling to see the advantage of S Plan, although I have seen a
number of posters supporting this.

Currently I have S plan, but will have boiler replaced shortly and
need to relocate solenoid valve/pump in existing system.

Currently the program is set for 1 hour water heating only before main
heating phase only at start of day.
1 hour water heating mid-day.
In the evening we have 6 hours heating with 1 hour water heating
included.
Would a Y plan system compromise this in any way or am I missing
something here?

TIA

Phil

They both do exactly the same job, and both give independent control over CH
and HW.

The main disadvantage of Y-Plan is that virtually all the control logic is
built into the 3-port valve's actuator - and if you've read this NG for a
while you'll have seen miriads of posts about all manner of CH woes, with a
large number of them being a problem with the 3-port valve.

As Christian says, S-Plan is much simpler to understand and also provides
volt-free contacts - with the valve motor drive and boiler/pump switching
being totally isolated from each other. However, if your boiler controls the
pump in order to provide pump-overrun, you're more likely to need a by-pass
valve on an S-Plan system.

Given a free choice (which I don't have because I inherited a Y-Plan
system!) I'd go for S-Plan every time. Yes I could (and still may!) convert
it.
--
Cheers,
Roger
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