I have a recurring problem with the radiators on the upper floor of my
house. From experience I have de-sludged and inhibited them in late
autumn but still the upper system chokes around this time of year and
the radiators go cold. On the ground floor all pipework is 22 mm and 15
mm copper (no problems there). However, on the 1st floor it is 22 mm
copper to and from a manifold and then 10 mm microbore.
My problem is this. Am I right in thinking that the flow and return
lines should serve two seperate manifolds? My system has them both
flowing through one manifold with the 10 mm microbore flowing and
returning from it. Is this right? I would have thought that the water
would follow the easiest route i.e. by-passing the radiators and
flowing straight back to the boiler. I think that as soon as I get any
sort of sludge in the microbore then that is exactly what is happening.
Every radiator in the house has a thermostatic valve, not a lockshield
in sight. No sign of a PRV anywhere else in the system either. I take
it from that, that the single manifold in question is not some sort of
internally divided job and it is 'straight through'. Coming to the
point now....Should I split the line here and install two seperate
manifolds and some sort of pressure relief between flow and return?

On 12 Mar 2006 13:05:19 -0800, "Alister21"
wrote:

I have a recurring problem with the radiators on the upper floor of my
house. From experience I have de-sludged and inhibited them in late
autumn but still the upper system chokes around this time of year and
the radiators go cold. On the ground floor all pipework is 22 mm and 15
mm copper (no problems there). However, on the 1st floor it is 22 mm
copper to and from a manifold and then 10 mm microbore.
My problem is this. Am I right in thinking that the flow and return
lines should serve two seperate manifolds? My system has them both
flowing through one manifold with the 10 mm microbore flowing and
returning from it. Is this right? I would have thought that the water
would follow the easiest route i.e. by-passing the radiators and
flowing straight back to the boiler. I think that as soon as I get any
sort of sludge in the microbore then that is exactly what is happening.
Every radiator in the house has a thermostatic valve, not a lockshield
in sight. No sign of a PRV anywhere else in the system either. I take
it from that, that the single manifold in question is not some sort of
internally divided job and it is 'straight through'. Coming to the
point now....Should I split the line here and install two seperate
manifolds and some sort of pressure relief between flow and return?

I suspect that you will find that this is actually a manifold with two
separate flow and return sections.

Try measuring or feeling the temperature of the pipes feeding it on
the boiler side and those going to the radiators.
If it really were going in and out as you say, there would be little
or no flow through the radiators, even when they are clean.



Does everything work OK immediately after cleaning? If not, then there
is probably a balancing issue and the radiators on the 15mm sections
need to have their flow reduced.

Certainly there should be lockshields on all radiators even if TRVs
are used, or the radiators on 15mm connections will probably receive
most of the flow until those rooms are warm.


If it deteriorates after a while and that is sludge, then there is
something else wrong. If you are using inhibitor, then it should
last for at least a year assuming you are using enough. There should
be little or no sludging. Even 8mm microbore works perfectly well
over long periods of time.

Suspects for early failure of the inhibitor and sludging would be
pumping over or sucking down of air in the feed/expansion tank. Have
you checked this carefully? Pumping over is obvious. Sucking down
will usually cause a sound of air bubbles being pumped around and it
will collect in the radiatrors.



--

..andy

The message .com
from "Alister21" contains these words:

manifold and then 10 mm microbore.
My problem is this. Am I right in thinking that the flow and return
lines should serve two seperate manifolds? My system has them both
flowing through one manifold with the 10 mm microbore flowing and
returning from it. Is this right?

You sure it isn't one block with two passages, one flow, one return?

--
Skipweasel
Pay no attention to the man behind the curtain.

Thanks Andy. One of your points has me thinking. This 'sucking down'
thing. I once cracked the upstairs bleed valves with the pump running
(bad practice I know). The needle valves sucked in air rather than
released water. Is this syptomatic of the problem you quoted or would
you expect that to happen every time? And if it is a sucking down
problem how can it be remedied / prevented?

Al.

"Andy Hall" wrote in message
...
On 12 Mar 2006 13:05:19 -0800, "Alister21"
wrote:

Suspects for early failure of the inhibitor and sludging would be
pumping over or sucking down of air in the feed/expansion tank. Have
you checked this carefully? Pumping over is obvious. Sucking down
will usually cause a sound of air bubbles being pumped around and it
will collect in the radiatrors.


Generally there can be 3 problems

1 Pump-over during normal running - disaster!

2 Pump-over when pump starts.

3 Pump-over when the pump stops.

I'd have said "suck down" is less likely because of the head of water which
has to be overcome for it to happen.

Any of the 3 will aerate the water with obvious consequences.

Guy,
I have never broke the line there as I did not want to disturb all
those 10mm joints. If memory serves (two winters since last I looked)
it is a cast unit and may well be internally divided. Andy suggests
that I feel both sides for a temperature drop and I will probably do
that next weekend.
Has anyone ever came across a manifold like this?
Al

On 12 Mar 2006 13:37:45 -0800, "Alister21"
wrote:


Thanks Andy. One of your points has me thinking. This 'sucking down'
thing. I once cracked the upstairs bleed valves with the pump running
(bad practice I know). The needle valves sucked in air rather than
released water. Is this syptomatic of the problem you quoted or would
you expect that to happen every time? And if it is a sucking down
problem how can it be remedied / prevented?

Al.


That is concerning because the system should always be under positive
pressure, even with the pump running. You could have air being
sucked in through a radiator vent somewhere, for example.

Is the Feed/expansion tank in the loft, one floor up from the highest
radiator?

Can you do a description of the relative positions of the boiler,
pump, motorised valve(s), the feed/expansion pipe, the vent pipe,
where the returns from the CH and cylinder coil connections join etc.?

It's not uncommon for items to be placed in the wrong order. A
classic is for the FE pipe and the vent pipe to be on opposite sides
of the pump or separated by more than 150mm or so of pipe - e.g.
opposite sides of the boiler. That's the kind of thing that can
cause the pump over/suck-down issues, although sometimes they are
subtle.

If you have a way to do a sketch and post on a web site somewhere it
would be ideal. The more information the better.




--

..andy

Excuse my ignorance lads but please explain 'pump over' / its causes /
its cure.

Thanks for all replies to date.
Al.

On 12 Mar 2006 13:44:35 -0800, "Alister21"
wrote:

Guy,
I have never broke the line there as I did not want to disturb all
those 10mm joints. If memory serves (two winters since last I looked)
it is a cast unit and may well be internally divided. Andy suggests
that I feel both sides for a temperature drop and I will probably do
that next weekend.
Has anyone ever came across a manifold like this?
Al


Yes.

I've seen them with a 22mm compression fitting at each end and a
different type with both 22mm fittings at one end with branches on
each side.

They don't seem to be so easily available any longer in these designs,
possibly because of the cost. More typical are brass blocks with 3
or 4 holes for 10mm or 8mm tubes. These are inserted into a 22mm
fitting and the lot soldered.

e.g. http://www.bes.ltd.uk/products/149b.asp


--

..andy

Andy I will need to do some scrambling about but basically the boiler
is on ground floor (kitchen). The pump is under the ground floor - I
think there is a motorised valve down there as well. The hot water tank
is on the first floor. The expansion tank is in the loft one floor
above the highest radiator.

Sorry it is very general but as I say the rest I will need to refresh
my memory with regard to the rest.

Al.

On 12 Mar 2006 13:53:36 -0800, "Alister21"
wrote:

Excuse my ignorance lads but please explain 'pump over' / its causes /
its cure.

Thanks for all replies to date.
Al.



See other post.

Basically it normally results from the pressure head between the FE
and vent pipes being too high because they are wrongly positioned.
However, there are scenarios where other places can be under negative
pressure as you have seen.


--

..andy

On 12 Mar 2006 14:11:13 -0800, "Alister21"
wrote:

Andy I will need to do some scrambling about but basically the boiler
is on ground floor (kitchen). The pump is under the ground floor - I
think there is a motorised valve down there as well. The hot water tank
is on the first floor. The expansion tank is in the loft one floor
above the highest radiator.

Sorry it is very general but as I say the rest I will need to refresh
my memory with regard to the rest.

Al.


OK.

I suspect that the devil might be in the detail here, but from what
you've said, I think that we are looking at air getting into the
system if it's OK immediately after cleaning and then deteriorates in
a few months.


--

..andy