On 09/01/2018 17:38, Chris B wrote:
This is a long rambling post for which I apologize, but If I just come
in with some questions there will inevitably be requests for more info
so I have tried to include all relevant info in one post.

As some of you will be aware I am helping a friend who has inherited a
house needing lots of updating. The central heating being one such
component.

The system was designed and installed by the now deceased owner who
helpfully kept lots of notes. There are extensive notes on
maintenance/repairs and changes from its installation in 1976 until
about 2005, but no record of any work since 2005. I'm sure that in its
heyday it was well maintained but that very little will have been done
to it in the last ten years.

As of now the DHW works fine (if somewhat uneconomically) but the room
heating system is completely broken, taking several hours to increase
the house temperature by a couple of degrees. The radiator temperatures
never get much above "slightly above cold", and by feeling the water
temperature around the CH pumps and comparing to the DHW pump I am sure
that there is very little water circulation round the radiators.

At the end of the heating season I intend to drain, remove all
radiators, flush, remove pumps and assess but before I even start I want
to make sure that I fully understand the system and make sure that I
take the right course of action. (It might be time to remove all active
components and start again - although this would probably be beyond my
DIY skills -but at least if I understand the system I can have an
intelligent discussion with a professional).

Having looked at the DIY FAQ pages what I think I have is an "S Plus
Pump Plan" ie exactly what we have here
http://wiki.diyfaq.org.uk/index.php/...s:_S_Plus-plan


but with the zone valves replaced with pumps and what he called "clack
valves" (of which more later).

The control system looks like a home brew box of relays and diodes.
Perhaps some pictures would help. (control box links lower down)

https://www.dropbox.com/s/vgvvcdyxlm...ntrol.jpg?dl=0

https://www.dropbox.com/s/4zrocgzq81...nstrs.jpg?dl=0


Now to my mind the radiators are not getting warm because
1) They are blocked - removal and off site flushing should solve this.
2) The pumps aren't pumping - they are either A) blocked or B) not spinning
A) Blocked - I have found info on diy faq about stripping and removal of
corrosion products from the impeller (more time consuming but cheaper
than a simple swap - time is not an issue).
B) Not spinning - How do I tell? - Simple 1:1 replacement may be
difficult see below.
3) Some other blockage.
Now this is where we come to the "clack valves". Or to give them their
correct title "Null Flow valves". (Leaflet courtesy of his extensive
records)

https://www.dropbox.com/s/5qxmapfy1s...valve.jpg?dl=0

There is a record of one of these jamming open causing " the landing
radiator getting hot when only the DHW pump was running". It was
stripped and rebuilt.
I can see from the "S Plan plus pump" schematic that if you replace the
zone valves with pumps then when only one pump is running there is
nothing to stop back-flow in the other loops.

Can these jam shut?

I'm afraid google has not been my friend and I can find no reference to
"clack valves" in modern heating systems. The only reference to NRV
seems to be in relation to those fitted to incoming mains supply pipes.

If these are jammed shut I can find no on line replacements. The chances
of getting an overhaul kit for these valves today must be just about zero.

Also the control box seems to be an aladdins cave of relays and diodes.
Failure of one or more of these components is of course a possibility.

https://www.dropbox.com/s/zm6ung9y1u...rnals.jpg?dl=0
https://www.dropbox.com/s/ksj3mh8wv7...x_pcb.jpg?dl=0
https://www.dropbox.com/s/sae3oudvgb...iring.jpg?dl=0


As far as I can see the design of the control box necessitates mods to
the pump wiring circuit board.

https://www.dropbox.com/s/wqdjodrxnh...tions.jpg?dl=0


It has taken me days wading through loads of old notes (note all images
are of his notes, I have not created anything new), would this system be
bread and butter to a current plumber/heating fitter or would they throw
up their hands in horror?

In the interests of future maintainability is it time to consider
replacing the 3 pumps with one, removing the "clack valves", installing
three zone valves, upstairs and downstairs programmable thermostats and
doing away with the magic control box box of relays and diodes?
(Although this will probably be a job for a professional rather than me)


This wont be started until the end of this heating season but any help
welcome.



Well, it certainly isn't a *conventional* S-Plan+ system. That, as you
have noted, would have a single pump and one zone valve for each zone
(3-in total). It would be wired so that the appropriate zone valve would
open whenever its zone was calling for heat, and so that the boiler
would fire and the pump would run whenever one or more zones were
calling for heat.

To achieve the same thing with a pump for each zone, but no valves,
requires some relay logic to run the boiler whenever one or more pumps
are running. Presumably that's what the control box - with its
assortment of diodes and relays - sets out to achieve, but I can't quite
get my head around how it does it. [One place where it differs from
S-Plan is that it appears to prevent the DHW from heating whenever
either or both of the heating zones are calling for heat. If you wanted
to convert to S-Plan+ but keep that feature, you'd have to make it
non-standard.]

The only application I've come across for null-flow valves is to prevent
gravity circulation in a pumped system. My first CH system was gravity
HW and pumped CH - and the upstairs radiators tended to get warm in the
summer when the boiler was just on for the HW and the pump wasn't
running. So I inserted what we affectionately called a "foo-foo valve"
in the upstairs circuit. This had a flap which could be opened by pump
pressure but not by gravity circulation pressure - thus preventing
gravity circulation.

As others have said, your problem is probably either with the pumps or
with silting up of the system. The pumps can be checked fairly easily.
It's worth checking that you've got a water path to each side of each
radiator by bleeding it with each valve closed in turn until you get a
flow of water through the bled hole.

A couple more thoughts . . .

It's presumably a vented system with a fill & expansion tank in the
attic? Could that have run dry (if its ball valve stuck shut) allowing
air to enter the heating circuits? Air locks would certainly prevent any
decent flow.

Are there any manual valves - e.g. for balancing the flow in the 3
circuits, or for maintenance purposes? Gate valves in particular are
notorious for jamming shut - even when the spindle appears to turn.
--
Cheers,
Roger
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