See my previous thread; a couple of you mentioned "pumping over".
What are the most likely causes of this?

I've posted of pics of the heat exchanger 24 hours after the leak at
http://www.ausn67.dsl.pipex.com/ideal_boiler.htm . Some of the images
of the underneath look fairly rusty, although it looks worse in the
photos than in real life. Is this normal? Presumably the burners are
underneath the heat exchanger, and condensation from the gas can
occur.
--
Hugo Nebula
"If no-one on the internet wants a piece of this,
just how far from the pack have you strayed?"

Hugo Nebula wrote:
See my previous thread; a couple of you mentioned "pumping over".
What are the most likely causes of this?

There are 2 things relevant to this;

1) Pressure is proportional/equivalent to the head of water. Old
pressure gauges used to be called altitude gauges and were calibrated
in both psi & feet head of water.

In metric units Pressure = density x g x head.

If you attached transparent pipes to a water system, the vertical level
of water would be proportional to the static pressure at that point.

2) When you have water flow through a system, there is a loss of
pressure/head caused by the frictional resistance of the pipes and
fittings. If you attached transparent pipes to a water pipe, the
vertical level would be proportional to the static head at that point,
as before, and the vertical level would drop as you progress along the
pipes in the direction of flow. Pumps add head/pressure to a system.




With an open system, there are usually 2 vertical pipes attached,
namely the open vent & the cold feed. If there is a lot of pipe and
fittings between the two connections there will be a large differential
pressure/head between the two connection points. If this head
difference exceeds the height of the open vent above the F&E tank water
surface, then water will flow up the open vent and down the cold feed.
This will churn up the water, dissolve oxygen from the atmosphere and
cause rapid corrosion.

The usual situation is that the cold feed is on the boiler return,
upstream of the pump, and the open vent is on the boiler flow,
downstream of the pump. The pump creates a large head difference
between the two connections and pumping over is more likely.

In article ,
Hugo Nebula abuse@localhost wrote:
See my previous thread; a couple of you mentioned "pumping over".
What are the most likely causes of this?

Usually the pump being at too high a speed. Set it on minimum and check
the rads furthest away still get hot. If not, go up a notch. If it still
pumps over on minimum with all the TRVs closed, come back for more help.

--
*It is easier to get older than it is to get wiser.

Dave Plowman London SW
To e-mail, change noise into sound.

In an earlier contribution to this discussion,
Hugo Nebula abuse@localhost wrote:

See my previous thread; a couple of you mentioned "pumping over".
What are the most likely causes of this?

Too high a pump speed, or incorrect connection of the fill and vent pipes.
[These should be connected into the flow pipe *before* the pump - and not
more than 6" from each other.]

I've posted of pics of the heat exchanger 24 hours after the leak at
http://www.ausn67.dsl.pipex.com/ideal_boiler.htm . Some of the images
of the underneath look fairly rusty, although it looks worse in the
photos than in real life. Is this normal? Presumably the burners are
underneath the heat exchanger, and condensation from the gas can
occur.

From your photos, its looks to me as if the heat exchanger has rusted from
the *outside* inwards - rather than from the inside outwards - so that the
black water may not have been too much of an issue. I suppose that if it has
been fired up a lot of times without really getting hot - maybe in response
to a frost stat in an unoccupied house - condensation *could* be the cause
of the corrosion.
--
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is invalid.

From your photos, its looks to me as if the heat exchanger has rusted from
the *outside* inwards - rather than from the inside outwards

Where is the corrosion with respect to the connections? The return
connection would be coolest and this is where on ewould expect most
condensation and corrosion to occur.

On Tue, 20 Sep 2005 14:47:39 +0100, a particular chimpanzee named "Set
Square" randomly hit the keyboard and produced:

From your photos, its looks to me as if the heat exchanger has rusted from
the *outside* inwards - rather than from the inside outwards - so that the
black water may not have been too much of an issue. I suppose that if it has
been fired up a lot of times without really getting hot - maybe in response
to a frost stat in an unoccupied house - condensation *could* be the cause
of the corrosion.

It was installed in July without a room 'stat, so it would be firing
continuously from the start of the heating season until I fitted one
in October; my mum went into hospital in January for 6 months, so we
set the 'stat to a low (16°C) setting until she came out. It would
have been firing up one a day for the hot water cylinder (which we
kept on). Is this long enough to corrode a cast iron heat exchanger?
--
Hugo Nebula
"If no-one on the internet wants a piece of this,
just how far from the pack have you strayed?"

In an earlier contribution to this discussion,
Hugo Nebula abuse@localhost wrote:


It was installed in July without a room 'stat, so it would be firing
continuously from the start of the heating season until I fitted one
in October; my mum went into hospital in January for 6 months, so we
set the 'stat to a low (16°C) setting until she came out. It would
have been firing up one a day for the hot water cylinder (which we
kept on). Is this long enough to corrode a cast iron heat exchanger?

Dunno! There's clearly something dire been going on. I wouldn't have
believed that a new boiler could get in that state in 14 months whatever you
did to it.

I suppose you are sure that it *was* new when it was installed - and that
the plumber wasn't passing off a used one as new?
--
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is invalid.