CH Pumped Return OK?
 

Hi all

My present S Plan CH system has a pumped return rather than flow - is there
any reason why I should swap?
I am getting quotes for a replacement condensing boiler and intend to do
some re-piping at the same time. Does this have any impact on the answer to
the above question? ie pumped return OK with new style boilers?

The system currently suffers from pump-over which I would like to resolve.
As the pump is in the return to the boiler, the feed to the upstairs HW
cylinder continues past the cylinder to become the vent pipe. The motorised
valve connection to the cylinder is teed off this flow line, so does not
obstruct the clear vent. But the water make-up into the primary circuit
connects to the return from the cylinder coil. So, if the hot water
motorised valve closes, it effectively separates the vent from the water
make up (this I believe may be causing the pump over).
Is there any reason why I shouldn't move the water make up connection to the
other side of the HW valve? This would position it in the flow/vent line
close to the tee for the cylinder coil supply. If I do this, it would be
similar to a combined feed and vent arrangement, but with the feed entering
at HW cylinder level rather than at the header tank IYSWIM.

Hope this lot is clear

TIA

Phil

CH Pumped Return OK?
 

On Thu, 29 Jun 2006 15:47:51 +0100, TheScullster wrote:

I am getting quotes for a replacement condensing boiler and intend to do
some re-piping at the same time. Does this have any impact on the answer to
the above question? ie pumped return OK with new style boilers?

Is there any reason why you aren't having a sealed system? It would make
life a lot easier for yourself and simplify the heating system. Also, low
water content boilers tend to operate better (quieter) on a sealed system
anyway.

Martyn

--
Geosolar, Cambridge. Gas central heating installations.
High quality ATAG boilers www.geosolar.co.uk

CH Pumped Return OK?
 

"Martyn Pollard" wrote


Is there any reason why you aren't having a sealed system? It would make
life a lot easier for yourself and simplify the heating system. Also, low
water content boilers tend to operate better (quieter) on a sealed system
anyway.

Thanks Martyn

I am hoping that someone with serious experience of vented systems will
comment here!
If I can stabilise the system and prevent the pump over, modifying the
existing layout will be the most "comfortable" route.

Yes I have considered/am considering a sealed system, but I am concerned
about the age and state of the piping and its ability to cope with increased
pressure. The ground floor is solid concrete with buried pipes and some
plastic has been introduced upstairs (not sure if it's barrier quality).
The original install is 1970s and this is probably the worst period in UK
history for build and service quality IMHO.

Phil

CH Pumped Return OK?
 

On Fri, 30 Jun 2006 08:28:17 +0100, TheScullster wrote
(in article ):


"Martyn Pollard" wrote


Is there any reason why you aren't having a sealed system? It would make
life a lot easier for yourself and simplify the heating system. Also, low
water content boilers tend to operate better (quieter) on a sealed system
anyway.

Thanks Martyn

I am hoping that someone with serious experience of vented systems will
comment here!
If I can stabilise the system and prevent the pump over, modifying the
existing layout will be the most "comfortable" route.

Yes I have considered/am considering a sealed system, but I am concerned
about the age and state of the piping and its ability to cope with increased
pressure. The ground floor is solid concrete with buried pipes and some
plastic has been introduced upstairs (not sure if it's barrier quality).
The original install is 1970s and this is probably the worst period in UK
history for build and service quality IMHO.

Phil




I've installed and worked on both and migrated from a vented to a sealed
system.

- If you want to retain an open vented system, then the solution to pumping
over is to make sure that the vent and feed/expansion pipes join the circuit
close together (within 150mm); or more conveniently use an air separator like
a Myson Aerjec to do the hookup. The important things to avoid are
certainly having them connect on opposite sides of the pump and almost
certainly on opposite sides of the boiler. Putting both on one side of the
boiler avoids the pressure differential that can otherwise arise.

- Making a system sealed does not mean that you are taking it up to mains
water pressure or anywhere close. You are going to take it from around 1bar
to 1.5 to 2bar. If the pipes are going to have a problem with this (which
I think is very unlikely), then it won't be long before they do with a vented
system.

- If there is going to be an issue, it is more likely to be radiator valves
leaking and seeping around the stems. As part of a system refurbishment, it
would make sense to proactively swap these out anyway. The system is going
to need a thorough cleaning, and the summer is the perfect time to take the
radiators outside for a thorough pressure wash. The whole process of doing
that and swapping valves can easily be done in a day.

- This cleaning should be done regardless of whether the system remains open
vented or goes sealed. What I did last time was to take the old boiler out
of service (switch off but leave installed), swapped in the sealed system
components. Then I had mains pressure available to flush the pipes as the
radiators were removed. Considering you have buried pipes downstairs, this
would be a good way to get the crud out of them.

CH Pumped Return OK?
 

"Andy Hall" wrote


I've installed and worked on both and migrated from a vented to a sealed
system.

.............snip

Many thanks once again for such an informative response Andy.
Can I prevail on your time/kindness and ask you to look at the schematic
http://www.thesculls.freeuk.com/CHScheme.jpg please?
This shows the flow from the boiler to the vent and the relative position of
the make up feed.
It looks like I do indeed have the worst case when the hot water motorised
valve is shut. With the valve shut, both the pump and the boiler are
"between" the fill and vent connections. ie fill to pump suction, vent after
pump and boiler.
To get around this, can you see any problem with moving the fill to the
point where the water tees from the flow/vent to the h/w cylinder?
This looks like it would create an arrangement close to a combined fill/vent
but not quite.
(The schematic shows system items at approx the right relative elevations).

Thanks again

Phil

CH Pumped Return OK?
 

On Fri, 30 Jun 2006 14:12:57 +0100, TheScullster wrote
(in article ):


"Andy Hall" wrote


I've installed and worked on both and migrated from a vented to a sealed
system.

............snip

Many thanks once again for such an informative response Andy.
Can I prevail on your time/kindness and ask you to look at the schematic
http://www.thesculls.freeuk.com/CHScheme.jpg please?
This shows the flow from the boiler to the vent and the relative position of
the make up feed.
It looks like I do indeed have the worst case when the hot water motorised
valve is shut. With the valve shut, both the pump and the boiler are
"between" the fill and vent connections. ie fill to pump suction, vent after
pump and boiler.
To get around this, can you see any problem with moving the fill to the
point where the water tees from the flow/vent to the h/w cylinder?
This looks like it would create an arrangement close to a combined fill/vent
but not quite.
(The schematic shows system items at approx the right relative elevations).

Thanks again

Phil



I had a similar arrangement to what you are describing when the system was
open vented except that the pump was on the flow side after the vent tee and
before the motorised valves.

If you're going to do this feed repositioning, I would use an air separator
like the Myson Aerjec. www.bes.ltd.uk part no. 11334.

Mine was set up like the third diagram, although any will work.
The fittings are copper tails which will go into any solder fitting.

The other advantage of these is that it makes initial filling/venting of the
system much easier since the small bubbles of air that initially tend to
circulate with the water can escape easily through the vent and tend to end
up less in the radiators.

CH Pumped Return OK?
 

"Andy Hall" wrote


I had a similar arrangement to what you are describing when the system was
open vented except that the pump was on the flow side after the vent tee
and
before the motorised valves.

If you're going to do this feed repositioning, I would use an air
separator
like the Myson Aerjec. www.bes.ltd.uk part no. 11334.

Mine was set up like the third diagram, although any will work.
The fittings are copper tails which will go into any solder fitting.

The other advantage of these is that it makes initial filling/venting of
the
system much easier since the small bubbles of air that initially tend to
circulate with the water can escape easily through the vent and tend to
end
up less in the radiators.

Thanks a lot Andy
I will have a look and see how this would map-in to the existing piping

Phil