On Sat, 16 Dec 2017 03:08:12 +0000, John Rumm wrote:

On 15/12/2017 22:34, Johnny B Good wrote:

I've been following the recent thread on "Heating system motorised
valve
questions" started by John Smith, with some interest. Although his
setup is obviously based on the classic S plan using a couple of two
port valves in place of the classic Y plan's use of a Honeywell V4073A
3 port mid position valve, John Rumm's post referencing the DIY wiki on
the various CH system control plans caught my attention with the 'Y'
plan plumbing schematic.

It's quite obviously an extremely simplified schematic, devoid of the
typical niceties of flow balancing valves and bypass pipework with flow
restriction valves which lead me to taking a closer look at my own
fully

Indeed, for the purposes of that article it only seeks to show how the
zone values function in the system.

However it does in a way highlight that we possibly don't have a good
diagram in their of the canonical vented DHW system. Perhaps someone
ought to draw one ;-)

We do have one for a heat bank:

http://wiki.diyfaq.org.uk/index.php/DIY_Heat_Bank


pumped Y plan system to compare against the various plumbing
arrangements shown in the "Ideal Mexico Super CF.65, 75, 80, 100, & 125
Conventional Flue Gas Boilers Installation & Servicing guide",
published November 1983 [1] which had been left by the local Gas
Central Heating firm we'd used.

There were a few interesting 'departures' from the fully pumped
system
plumbing arrangements for the boiler connections shown in that
installation and servicing guide which raised a few questions I'd like
to present to the cadre of Central Heating Experts that frequent this
NG.

The wiki article tends to stick to the examples in the Honeywell
"standard" docs.

[snip]

Compared to the Y Plan plumbing circuit shown in the wiki http://
wiki.diyfaq.org.uk/index.php/File:Y-Plan-Water.gif there is a gate
valve on the flow side plumbing between the mid position valve and the
upper heat exchanger coil port on the hot water tank, obviously there
to balance the flow when calling for both heat and HW.

Yup quite commonly done since otherwise the cylinder's HE could starve
the rads of flow due to it being a very low resistance. (making it
behave more like a W plan system). This would be fine with a modern fast
recovery cylinder than can swallow the full output of the boiler, but
not good a traditional cylinder that will max out at say 5kW transfer
rate. Then you just leg loads of boiler cycling, and no heating for as
long as it takes the cylinder to slowly lumber its way up to its set
point.

However, in addition,
there is also a valved shunt (15mm pipe) tapped into the pump outlet to
the AB port of the 3 port valve 28mm pipe and the HW H/E coil return
which seems a little excessive of pump protection since the ground
floor shower room (adjacent to the utility room) has a heated towel
rail (previously a small radiator) with no TRV fitted to provide the
required safety shunt.

Probably a belt and braces... also to protect against future changes to
the bypass rad or the addition of any blocking elements (TRVs etc)

I'm not sure whether this departure from the guide (after some 30 odd
years of service) is important.

The fact that its been working (mostly) trouble free for 30 years would
indicate not ;-)

I can't see why there would have been any problems with such an
arrangement even though I did have to push a length of pyro down the
feed pipe from the attic to unblock it about a year or three after it
had been installed. This was a one off problem that's never repeated in
the subsequent 30 odd years so this plumbing variation does not appear
to be of any consequence, at least not in my case.

So, my questions a

Is my current header tank feed and expansion pipe arrangement
something
to be concerned about?

No. The only real concerns are systems where the vent gets scaled and
completely blocked, or where significant air is induced into the system
on a regular basis (either by "suction" on the vent, or by pumping over.
Then that will lead to massive corrosion problems, and lots of
"sludging" up.

and, is there any good reason not to close the bypass shunt between the
pump out flow and the H/E return?

Only the old adage "if it ain't broke, don't fix it!"

You'll notice from my other post that I seem to have already "fixed it"
about a year ago with no detrimental effect (so far!). :-)) (what's the
emoticon for 'foolish grin'?)


All in all, including two or three doses of Fernox MB1, I doubt I've
spent more than 350 quid in repairs/servicing over the past 35 years or
so since the system was installed so I can't complain. Looking at
others'
experience with "Modern Energy Efficient" Condensing Boiler systems,
I've saved far more on expensive repair costs than any savings in gas
consumption ever could.

It does rather depend on circumstances... on systems with very high gas
usage there is more upside to a modern system. I ripped and replaced an
ancient Ideal Mexico RS based system with a very poor vented DHW system
(really not well suited to the property at all) about 5 years ago. I
went to town with it and did fully weather compensated heating, split
into separate zones, unvented DHW etc. Even ignoring that the house is
now way more comfortable, and the DHW system is like a veritable heated
fire hose in performance as valid justifications for the hassle and
expense, its now also pretty much paid for itself in reduced energy
costs[1]. In that time its maintenance costs have been a couple of top
ups with Sentinel X100.

[1] When you consider the old system was probably throwing 35p of every
quids worth of energy I bought it straight out the flue...

Going by the burner heat input and water heat output figures, the boiler
had an efficiency of 79%. Not as impressive as the most efficient of
condensing boilers and probably lower with age by now but in this 3 floor
Victorian semi detached house, I suspect that the atypical length of flue
liner going up the basement chimney is reabsorbing at least half of that
waste heat back into the fabric of the house making a small but useful
contribution to the heating. Not all of that 21 to 30% of waste heat is
being vented straight out the top of the chimney stack in my case.

The outdated (outlawed?) cast iron lump's KISS principle of heating
seems to be a good match to the needs of this Victorian property. I'm not
overly keen on the high maintenance cost at any price for the improved
efficiency of a modern condensing boiler and its restriction on maximum
flow temperature, requiring higher output rads to compensate for the
reduction.

For this property at least, I don't believe I'd be better off in the
long run going over to an all in one modern compact boiler packed with
sophisticated features where the slightest leak could result in a very
expensive repair. Modern all in one boiler solutions seem to have been
designed to simplify installation and costs for the installer at the
expense of long term reliability costs being externalised onto the end
user.

My attitude might be more a case of "Better the Devil you know." than a
well reasoned calculation of the best solution but I've seen more than
enough reports in this NG of the problems with modern CH/DHW systems to
be confident that my best bet is to stick with the system I've already
got.

--
Johnny B Good