Y plan plumbing questions

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 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.
My system is laid out such that the boiler itself is installed in the basement with only 28mm flow and return pipes and the 22mm gas pipe plumbed into it and a multicore cable to the Potterton 2000 control panel in the ground floor utility room above.
There is no pipework associated with the header tank feed and vent connections as shown in the guide for a fully pumped system, those are plumbed into the airing cupboard pipework around the pump and 3 port mid position valve in the first half landing loo which is also the location of the switched FCU mains connection fed from the supply side connections of the immersion heater switched connection box[2].
The header tank, mounted as high as possible[3] in the attic, accessible via a door on the half landing above, is about 5 or 6 metres higher than the pump which is itself a good 6 or 7 metres above the boiler[4]. There are two drain down points in the system, an outside one to facilitate drainage of most of the system without resorting to the use of a bucket chain or a pump and one at the boiler itself to allow for a complete drain down whenever the need might arise.
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. 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.
I can't see a condition where such a shunt would be needed. The mid position valve can't block the flow unless the towel rail shield valve is closed *and every* TRV on all the other (12) radiators have closed when only heating is being called for. When only hot water is demanded, there is always a flow path via the H/E coil even if it may be restricted by the balance valve and, I assume, the boiler and pump will be shut off when the tank stat signals that the demanded temperature has been reached.
The only thing that might justify the presence of this additional shunt would be a misguided assumption on my part regarding boiler/pump shut down when only HW is selected and the tank has reached the set temperature.
The 15mm pipe header tank feed and the 22mm expansion pipe are both teed into the 28mm boiler flow feed to the pump (rather than, as suggested by the guide, the 2nd return and flow ports of the boiler itself) using a separate Tee adapter each, with a separation of about 5 inches along the 28mm pipe about 2 foot or so upstream of the pump inlet.
I'm not sure whether this departure from the guide (after some 30 odd years of service) is important. 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 are:
Is my current header tank feed and expansion pipe arrangement something to be concerned about?
and, is there any good reason not to close the bypass shunt between the pump out flow and the H/E return?
Any other comments?
=========================================================================Maintenance History and additional notes
Whilst this was installed by a local company some 35 years ago, I've never had a maintenance contract of any sort. The only servicing it received was on those rare occasions when the boiler itself stopped firing up due, in one case, to a worn out gas valve (Nov 1998) and in another case a faulty thermocouple (Dec 2012).
Aside from the 3 port valve failure and one leaking TRV, all the other problems have been pump related where the original "shitty" Grundfoss unit failed after some 6 or 7 years of service when I started using a different pump type supplied by my father where the stator windings are separated by an aluminium sheet from the rotor/impeller in the wet half of the pump body which kept giving me grief over the next 5 to ten years until I finally gave up and caved into buying another "shitty" Grundfoss which, to my surprise, turned out to be anything but "shitty" being almost completely silent in operation, unlike its predecessor, and remaining so to this day some ten years on.
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.
Incidentally, this system was never endowed with a room stat, relying instead on TRVs on all but one rad and the boiler stat alone. Although I could easily wire in a room stat, ICBA with one more thing to be twiddled with and go wrong plus, I think a weather sensor would be a more useful feature than a room stat.
The extra energy wasted by relying on the boiler stat and TRVs alone isn't going as much to waste compared to more conventionally located compact lightweight condensing boilers where such control of the heat would result in hothouse conditions in the room that's been afflicted by such a boiler. Mine being in the basement puts that 'wasted energy' to good use in maintaining a base level of heat in the rooms above.
[1] About a year before the system was installed, coincidentally just before the 3 port mid position valve assembly design was changed to the current type whereby the valve motor head can be detached without having to drain down the system. I discovered this when I finally decided, last year, to do something about the 1st floor rads warming up when only hot water was selected. Initially I was seeing prices for the whole valve assembly in the region of 120 to 160 quid. In the end, I was able to upgrade to the later design for a mere 67 quid (new valve plate and matching motor head -retaining the original brass valve body).
[2] The immersion heater had originally been fed via a switch with neon indicator in the utility room with an FCU for the immersion element in the airing cupboard. The switch and the FCU were swapped round to save having to run a spur off one of the ring main circuits to provide mains power for the CH controller. The only casualty of this rearrangement being the matter of convenience in controlling the immersion heater which was now only required in the event of a CH/HW system failure.
[3] The extra height was needed to service the 2nd floor rads the tops of which are only a metre or so below the header tank water line.
[4] The basement was the obvious location as far as I was concerned since I was using it as a radio shack and a workshop which would benefit from the extra heat and save using up valuable living space elsewhere. Also, I realised that the higher static water pressure would hold any kettling tendencies at bay so a win-win situation all round.
True enough that it cost a little more in 28mm flow and return pipework (the heat loss into the ground floor above wasn't considered an extra burden on running costs) some of which was compensated for by the shortened run of 22mm gas pipe required to connect to the consumer side of the gas meter pipework located across the other side of the basement.
--
Johnny B Good

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On Fri, 15 Dec 2017 22:34:16 +0000, Johnny B Good wrote:
====snip===

Having posted the original fulsome query. It's occurred to me that the point at which the overflow has been teed into the system is on the suction side of the pump which should make "pump-over" impossible.
Considering that the feed pipe from the header tank is likewise subjected to the same drop in pressure during pumping, there may be a small but transient 'draw down' from the header tank during pump startup with a corresponding small but transient back-flow when the pump shuts off.
Ignoring evaporation of the header tank water for the moment, the first draw down event will cause the ballcock to admit a little water to top it back up, thereafter, the level can vary without further admission of top up water. Since header tank water does evaporate, the ballcock will eventually operate to compensate for this loss.
Although the net effect on water consumption remains unchanged, the same can't be said for the corrosion inhibitor which will suffer a marginally higher rate of consumption, particularly of its anti-oxidant component as it becomes dispersed into the header tank where it can then be consumed by the dissolved atmospheric oxygen. The 3 or 4 metres of 15mm pipe between the header tank and its connection into the system plumbing will, however, act as a buffer zone with an inhibitor concentration gradient that will reduce the diffusion rate of inhibitor into the header tank.
I suspect I may be "over-thinking" this conundrum. Feel free to respond to this post rather than the previous one (it'll make quote trimming a doddle :-) ).
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Johnny B Good

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On 16/12/2017 01:02, Johnny B Good wrote:

It makes pump over less likely, but at the enhanced risk of drawing air into the system on installations which don't have much head above the point the vent tees off. (by the sounds of it, not something you need to worry about on yours).
(a good solution in those cases is to combine the F&E and Vent into one tee into the system, with the vent teed into the F&E pipe a few inches up from where it leaves the main primary circuit. That pretty much ensures the only thing that will get sucked in is water from the F&E tank)

Indeed. So long as you have left enough space between the set level in the F&E tank and its overflow.

This is a problem with any vented system, since even without the effects of the pump you will see significant flow into the F&E tank as the system heats (probably around 4L for every 100L of primary water in the system), and then flow out as it cools. So you are continuously cycling the system water the tank and exposing it to more atmospheric O2.

Agreed ;-)

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John.
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On 16/12/2017 01:02, Johnny B Good wrote:

Well yes, if it's still going strong after 30-odd years, I'm not quite sure what you're worried about.
If it were my system I would try to contrive that, under normal circumstances, the HW and CH are not being heated at the same time. You then wouldn't have to worry about HW vs CH balancing and could remove any restriction on the HW side, resulting in faster recovery. You could achieve that by using the existing programmer to time the HW, and inserting a programmable room stat to time the CH. [You really, really *should* have a room stat]. Then, you could heat a tank of water each morning before the CH comes on and, with a decently insulated tank, it should stay hot for a long time.
Judging by the age of your boiler, and the fact that it's got two lots of connections, it was probably designed with gravity HW and pumped CH in mind. In that case, the boiler capacity will be such it's own stat can stop it overheating without requiring pump over-run or a minimum flow rate. You should certainly be able to do away with a pipe which by-passes the HW coil.
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Roger
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On 16/12/2017 17:30, Roger Mills wrote:

Worth keeping in mind that a cylinder of that age may be relatively slow recovery by today's standards. So heating just the cylinder may require lots of cycling on the boilers stat.
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On 16/12/2017 19:55, John Rumm wrote:

Fair comment, if it's the original cylinder. I don't think the OP said he's ever replaced it, but he may have forgotten. If it *is* original, it's lasted pretty well. [I'm on my third cylinder in 40 years]. Not only will the coil surface area be a lot lower than more modern cylinders, but the heat transfer capacity will likely have been reduced further by scale build-up - unless it's in a soft water area.
If all that is the case, maybe there is some point in heating the HW and CH concurrently, with the HW side throttled back a bit - but I still don't see any need for the by-pass.
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On Sat, 16 Dec 2017 20:23:34 +0000, Roger Mills wrote:

The Stelrad Group installation and maintenance guide the CH installers left with me certainly shows the use of the extra ports to create a gravity HW and a pumped CH system. It doesn't offer much detail about what happens to the extra ports when plumbed as a fully pumped CH & HW system though. I guess the guide is aimed at any visiting engineers who may be tasked with repair or maintenance work rather than the DIY minded householder.

As a matter of fact, that was the only component *not* supplied by the CH installers since it had already been installed by the previous owners, complete with the H/E coil already fitted but unused. The engineer checked it over and was quite happy to plumb it into the system.
Judging by the fact that it's still going strong some 35 years on, I'm guessing it must have been installed not long before the previous owners put the house on the market. The connecting pipework is in 22mm, possibly matching the heating coil diameter (just a guess on my part).

Not a soft water area but Istr seeing a report on the quality of our water supply. I can't recall the details other than it wasn't particularly poor in regard of water hardness which seems to be borne out by the slow rate at which the 3KW electric jug kettle has only partially furred up its H/E base plate during the past year or so of hard use.

TBH, it's the bypass between the pump outlet pipe (*before* it hits the mid position valve) and the DHW H/E coil return that's the most puzzling arrangement in view of the fact there has always been one radiator, now a towel rail, without a TRV to act as a bypass in the event that all the other 12 rads are shut down by their TRVs.
I've just taken another quick look at the airing cupboard plumbing (I needed to take a piss anyway) and it occurs to me that it just might possibly be installed for the same reason that the motorised valve has a manual lever to lock it in the mid position when powered off to facilitate drain down / refill maintenance procedures.
Could this be a more likely possibility? I've just taken a look at the valve settings and I appear to have closed off the 'pump bypass shunt' and left the DHW H/E feed backed off a quarter of a turn from fully open some time ago, probably when I was sorting out the defective mid position valve last year. It looks like I may have already reached this conclusion, rightly or wrongly a year ago, and simply forgotten all about it.
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I'm going to hit just these problems shortly and would welcome advice/wiki info.
I opted for a thermal store rather than stress about Megaflow maintenance issues. (My insurers want annual inspections for pressure vessels, air compressors etc. so I can see where the interest lies.)
With underfloor heating and pretty much 24 hour occupation, I think priority could be given to hot water. The manifolds come with a local circulating pump but I assume a further circulating pump will be required. The combi we have for our annexe here must have an internal pump as the plumbers did not use the one supplied with the floor heating kit.
Pumping over is a concern as the make-up tank is below ceiling height (chalet bungalow).
I haven't yet met a plumber keen to take on the job!
--
Tim Lamb

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

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

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

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.

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

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

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.

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

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...
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On 16/12/2017 03:08, John Rumm wrote:

or even "in there"...
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On Sat, 16 Dec 2017 03:08:12 +0000, John Rumm wrote:

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'?)

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.
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