In an earlier contribution to this discussion,
Dave Osborne wrote:

Roger Mills wrote:

I would, however, query the comment which goes with C-Plan about
being completely obsolete and unsuitable for either new systems or
refurbishments. I agree about new systems, but there are still a lot
of gravity HW systems out there which would benefit from being
converted to C-Plan - which requires very little plumbing and
delivers considerable efficiency improvements relative to the status
quo. The only downside compared with a fully pumped system is that
when just HW is being heated, the boiler is on for longer than it
otherwise would be - albeit cycling on its stat rather than firing
continuously. Does anyone have any evidence that this does not meet
Part-L, and
would thus presumably be illegal as an upgrade from a 'conventional'
gravity HW/pumped CH system?

I found a website which stated this:

"Recent changes to the Building Regulations have made semi-gravity
non-compliant, so fully pumped is the only layout currently suitable
for new installations. The Building Regulations now control boiler
replacements too, and effectively require conversion of semi-gravity
systems to fully-pumped whenever a boiler is replaced."

Clearly, the author of the above doesn't cite his sources and I have
to say I didn't check them either. If you think the above statement is
********, then please let me know.


The statement, as it stands, may well be correct - but it doesn't cover the
situation where a zone valve is inserted into an existing gravity system to
convert it to a C-Plan *without* changing the boiler. I have occasionally -
via this NG - suggested that people should consider this option when they
complain either that the HW gets *too* hot or that they have to turn the
boiler stat down to prevent this - with the result that the rads are not hot
enough. A C-Plan system solves this problem by providing independent control
of HW and CH *and* provides a boiler interlock - ensuring that the boiler
switches off when both demands are satisfied.

Am I suggesting that they do something which is *illegal*?


I'm still not sure about the way in which Y-Plan's mid-position
valve is depicted. As everyone knows, it has two microswitches and
other components in addition to the motor. I still tend to the view
that we should either show *all* internal connections (as for other
types of valve) or *none* (as per Honeywell's original Y-Plan
diagram).

Ok, I thought about this. I am of the opinion that showing the full
internals of the mid-position valve would not be useful to the vast
majority of people and indeed, I couldn't draw it in the space
available at any reasonable scale. Also, I do not have such a valve
to hand to reverse-engineer the wiring details for. However, it is
clear from Honeywell documentation previously cited that the white
and grey wires assert the valve and the orange wire is a switched
output - which is what I have indicated on the schematic. I am
inclined to leave it as it is and I don't see a downside in doing so
- it is after all standard practice over a wide range of
electrical/electronic industries to show a simplified form of
internal operation of a device.

Fair enough - it's not a big deal.

I think you've done a great job with the diagrams!
--
Cheers,
Roger
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