[Johnny B Good]

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 a

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 "****ty" 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 "****ty" Grundfoss
which, to my surprise, turned out to be anything but "****ty" 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

[Johnny B Good]

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

====snip====


So, my questions a

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


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 :-) ).

--
Johnny B Good

[John Rumm]

On 16/12/2017 01:02, Johnny B Good wrote:
On Fri, 15 Dec 2017 22:34:16 +0000, Johnny B Good wrote:

====snip====


So, my questions a

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


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.

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)

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.

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

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.

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.

I suspect I may be "over-thinking" this conundrum. Feel free to respond

Agreed ;-)

to this post rather than the previous one (it'll make quote trimming a
doddle :-) ).


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

[John Rumm]

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!"

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...




--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

[John Rumm]

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

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 ;-)

or even "in there"...

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

[Roger Mills[_2_]]

On 16/12/2017 01:02, Johnny B Good wrote:
On Fri, 15 Dec 2017 22:34:16 +0000, Johnny B Good wrote:

====snip====


So, my questions a

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


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 :-) ).


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.
--
Cheers,
Roger
____________
Please reply to Newsgroup. Whilst email address is valid, it is seldom
checked.

[John Rumm]

On 16/12/2017 17:30, Roger Mills wrote:
On 16/12/2017 01:02, Johnny B Good wrote:
On Fri, 15 Dec 2017 22:34:16 +0000, Johnny B Good wrote:

====snip====


So, my questions a

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


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 :-) ).


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.

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.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

[Tim Lamb[_2_]]

In message , Roger Mills
writes
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.

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

[Roger Mills[_2_]]

On 16/12/2017 19:55, John Rumm wrote:
On 16/12/2017 17:30, Roger Mills wrote:
On 16/12/2017 01:02, Johnny B Good wrote:
On Fri, 15 Dec 2017 22:34:16 +0000, Johnny B Good wrote:

====snip====


So, my questions a

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


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 :-) ).


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.

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.


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.
--
Cheers,
Roger
____________
Please reply to Newsgroup. Whilst email address is valid, it is seldom
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[Johnny B Good]

On Sat, 16 Dec 2017 20:23:34 +0000, Roger Mills wrote:

On 16/12/2017 19:55, John Rumm wrote:
On 16/12/2017 17:30, Roger Mills wrote:
On 16/12/2017 01:02, Johnny B Good wrote:
On Fri, 15 Dec 2017 22:34:16 +0000, Johnny B Good wrote:

====snip====


So, my questions a

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


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 :-) ).


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.

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.


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.

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).



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.

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.


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.

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 **** 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.

--
Johnny B Good

[Johnny B Good]

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