Hi all
Have had a few happy weeks replacing the gas valve-boiler thermostat and one
motorised valve in my 1995 open circuit central heating system.
I now find the pump persists in getting air in it despite repeated system
bleeding.The local Corgi man announced that my system will always drag air
in.Its a conventional below the floor bungalow system with hot water tank at
floor level and top up tank in the attic.The pump is mounted at the top of
the boiler and the expansion pipe comes from a lower boiler tapping top up
is achieved by connection to hot water circuit at the inlet side.
I fail to understand where the air can gain access.
Can anyone clarify

hi,yer corgi man is at it,if your expansion pipe is coming off the bottom tapping on your boiler thats completely wrong for a start, and will not work at all in the result of overheating, thermostat failure etc, if the system is full of water the pump should create no problems, make sure when you bleed the system the header tank in the loft is filling, if it fails to fill, the feed to the heating system could be blocked which is quite common. meaning that your bleeding the system with no water replacing it and moving existing water around the system, failing that try an AAV (auto air valve) in the system. pacer

hi,yer corgi man is at it,if your expansion pipe is coming off the
bottom tapping on your boiler thats completely wrong for a start,

There is a choice of tappings 2 at the top and 2 at the bottom should the
expansion pipe be from the top.
The boiler was installed by heating engineers-not D-I-Y me. if the system is
full of water the pump should create no
problems, make sure when you bleed the system the header tank in the
loft is filling
The attic top up tank is filling and supplying ok.
The fill enters the system at the domestic hot water cylinder which is 7
feet from the expansion pipe-both are on the supply side of the pump-could
air be drawn in here.
Where do I fit the automatic air bleeder.

On Mon, 22 Aug 2005 11:21:57 GMT, "tom patton"
wrote:


hi,yer corgi man is at it,if your expansion pipe is coming off the
bottom tapping on your boiler thats completely wrong for a start,

There is a choice of tappings 2 at the top and 2 at the bottom should the
expansion pipe be from the top.
The boiler was installed by heating engineers-not D-I-Y me. if the system is
full of water the pump should create no
problems, make sure when you bleed the system the header tank in the
loft is filling
The attic top up tank is filling and supplying ok.
The fill enters the system at the domestic hot water cylinder which is 7
feet from the expansion pipe-both are on the supply side of the pump-could
air be drawn in here.
Where do I fit the automatic air bleeder.



You shouldn't normally need an automatic air bleeder, really Thomas.

I think you are using the term "expansion pipe" where it is really the
vent pipe. This is the one at the boiler, yes? The expansion is
dealt with through the feed/expansion pipe (which you are calling the
"fill").


At any rate, if you have 2m or so of pipe between the two, then this
can easily lead to air being drawn in, especially if the vent pipe is
closer to the pump inlet than the feed pipe. This is because there
will be a lower pressure at the point where the vent joins than that
at the F/E connection point.

One thing that you could try is to reduce the pump speed. This may
reduce the pressure differential to a point where air is no longer
sucked in. On the other hand, it may result in heat not being
transferred fast enough from the boiler and the house not warming up
enough.

A better solution would be to correct the plumbing. The vent pipe
and the feed/exp. pipe should be connected at a point where there is a
clear path from the boiler (i.e. no motorised valves in the way), and
close together. Ideally, that whould also be a high point to allow
any air to escape through normal flow and rising.

It's certainly not correct to have one going to the bottom of the
boiler and the other to an arbitrary point somewhere else. You have
places where air can be trapped.

One solution (I had this before converting my system to sealed
operation), is to take the flow pipe from the boiler, then in the
airing cupboard run it through an air separator (as described in
previous post), to which F/E and vent are connected; then to the pump
and following that to motorised valve(s) and the rest of the system.

Other combinations are possible. The key things a

- nothing in the way between boiler and vent
- vent and F/E pipes close together and ideally connected at a high
point to allow air to escape.


--

..andy

To email, substitute .nospam with .gl

ldn't normally need an automatic air bleeder, really Thomas.

I think you are using the term "expansion pipe" where it is really the
vent pipe. This is the one at the boiler, yes?

It is in 22mil copper goes vertically through the roof.

At any rate, if you have 2m or so of pipe between the two, then this
can easily lead to air being drawn in, especially if the vent pipe is
closer to the pump inlet than the feed pipe. This is because there
will be a lower pressure at the point where the vent joins than that
at the F/E connection point.
The vent pipe is 2 feet max from the pump the expansion pipe is more than 6
feet from the pump and now that I think about it its on the opposite side
from the vent ie the vent is on the pump feed side and expansion is on the
pumped side.The expansion also has a motorised valve between it and the
boiler.

Many thanks for your detailed reply Andy I can see that a bit of redesign is
needed here Im adding radiators anyway so will just readjust the expansion
and vent system at the same time.
Does nt the closed system not give a lot of problems--
short boiler life-top up problems-not enough hot water.

On Mon, 22 Aug 2005 16:52:23 GMT, "tom patton"
wrote:

ldn't normally need an automatic air bleeder, really Thomas.

I think you are using the term "expansion pipe" where it is really the
vent pipe. This is the one at the boiler, yes?

It is in 22mil copper goes vertically through the roof.

Oh dear, Thomas. The vent pipe should go up and loop over the
heating feed/expansion tank.




At any rate, if you have 2m or so of pipe between the two, then this
can easily lead to air being drawn in, especially if the vent pipe is
closer to the pump inlet than the feed pipe. This is because there
will be a lower pressure at the point where the vent joins than that
at the F/E connection point.
The vent pipe is 2 feet max from the pump the expansion pipe is more than 6
feet from the pump and now that I think about it its on the opposite side
from the vent ie the vent is on the pump feed side and expansion is on the
pumped side.

OK, so there's an even bigger reason. You are putting the whole pump
head and the pressure differential through the pipe in play, so not
surprising that air is entering.


The expansion also has a motorised valve between it and the
boiler.

That's not good either. Both the expansion and vent pipes should have
a clear path to the boiler.



Many thanks for your detailed reply Andy I can see that a bit of redesign is
needed here Im adding radiators anyway so will just readjust the expansion
and vent system at the same time.

Good opportunity. You might also want to look at giving the system a
thorough flush and clean.


Does nt the closed system not give a lot of problems--
short boiler life-top up problems-not enough hot water.


Do you mean sealed CH primary? No, not at all. Take a look at Ed
Sirett's FAQ on sealed systems - link in his signature. However,
check if your boiler is suitable. Is it actually 1955? If so, it
probably isn't anyway.

On your other comments, you may be thinking about condensing and combi
boilers of which there are one or two threads in this NG.

Briefly...... Early UK designed and made condensing boilers tended
to be done by adding a secondary heat exchanger to an existing design.
The problem is that the condensate is mildly acidic and if the design
doesn't account for it, the boiler corrodes.

Filling of sealed systems is not an issue as long as there are no
leaks. More in Ed's FAQ

Combi boilers have often been fitted as a one box solution. This can
be fine, but the pitfalls for the unwary are if the cold water supply
is inadequate and/or the boiler power too small. Some people like
mains pressure hot water. If you like that and the water flow is
good, then a thermal store is a good option and can produce HW at a
good rate as well. If you are tight on space and have modest to
average water requirements, a combi could be interesting. If you
need a lot of HW - e.g. larger house, 2 people, 2 or more bathrooms
with baths and showers then some form of storage will perform better.


--

..andy

To email, substitute .nospam with .gl

On Sun, 21 Aug 2005 16:32:48 GMT, "tom patton"
wrote:

Hi all
Have had a few happy weeks replacing the gas valve-boiler thermostat and one
motorised valve in my 1995 open circuit central heating system.
I now find the pump persists in getting air in it despite repeated system
bleeding.The local Corgi man announced that my system will always drag air
in.Its a conventional below the floor bungalow system with hot water tank at
floor level and top up tank in the attic.The pump is mounted at the top of
the boiler and the expansion pipe comes from a lower boiler tapping top up
is achieved by connection to hot water circuit at the inlet side.
I fail to understand where the air can gain access.
Can anyone clarify



It's usually sucked down the vent pipe.

This can happen if the vent pipe is on one side of the pump and the
feed/expansion pipe on the other, or simply if they are connected to
the circuit sufficiently far apart that a pressure differential is
created. The normal recommendation is 150mm max between the places
where these two pipes join the circuit.

If you are having difficulty, one solution is the Myson Aerjec, which
is a separator device that you put on the circuit and connect
feed/expansion and vent pipes to it. This brings everything close
together and also makes it easier for air etc to escape.

Another possibility is that the gas is actually hydrogen resulting
from corrosion. You are using inhibitor, aren't you?

Pumps are meant to be self purging, but will be less likely to trap
air or other gases if mounted with pipe vertically.


--

..andy

To email, substitute .nospam with .gl

tom patton wrote:
Hi all
Have had a few happy weeks replacing the gas valve-boiler thermostat and one
motorised valve in my 1995 open circuit central heating system.
I now find the pump persists in getting air in it despite repeated system
bleeding.The local Corgi man announced that my system will always drag air
in.Its a conventional below the floor bungalow system with hot water tank at
floor level and top up tank in the attic.The pump is mounted at the top of
the boiler and the expansion pipe comes from a lower boiler tapping top up
is achieved by connection to hot water circuit at the inlet side.
I fail to understand where the air can gain access.
Can anyone clarify


Hi Tom,

This sounds a bit like a problem I had a month or so ago caused by
sections without bleed facilities. Our solution after a week of
fighting it was so crude I'm embarrassed to tell you:

- stop the pump:
- bleed it.
- Disconnect boiler heating to prevent overheating (those extra
switches were SO useful.
- Open the bleed screw on the pump just a little. Run it with cold
water in the system and the air simply 'fizzles' out.
- when air stops bubbling, turn boiler on.

Boy did that air shoot out!! Loads of it with only about a teacup of
water lost. Took about 5 minutes to purge it and the system is still
running fine (correction: it was when I left this morning!).

Good luck. Tell us your eventual solution or any new tricks!

Phil