On Mon, 24 May 2004 19:25:46 +0100, "Ed Sirett"
wrote:

On Mon, 24 May 2004 16:26:20 +0100, Grunff wrote:

BigWallop wrote:

So, in summary, although I disagree with the suggestions you've made on the type
and construction materials of the pump required in the situation that the OP
(Harry) has

I think you've misunderstood the reasoning. In a CH system, the only
reason the iron/steel components (pump, rads, boiler water jacket etc.)
last more than a few months is that it's a closed system.

You start off with a set amount of water. In the first few weeks, all of
the oxygen in this water gets reacted out. The water by then has zero
dissolved oxygen, and is limited in the amount of corrosion it can cause.

But if you had a constant supply of fresh water the corrosion would
carry on at the same rate. Within a few months there weill be very
little iron left.

I have had mixed results with using iron pumps for DHW boosting and
circulation.
In two applications I replaced the previous iron with a new iron pump and
all was well. Perhaps the water heater had managed to undissolve all the air
from the water before it met the pump?
In the other application I was taken with the 'its wrong but its five times
cheaper and does the job' argument. I installed an iron pump only to have
to replace it with a bronze one a few weeks later due to discolouration of
the water.

Hi,

Installing some sort of anode upstream by the pump could help, BES
part no. 12242 might do though it's zinc and not magnesium which is
better. A section of 22mm or 28mm pipe with a nice big lump of
magnesium fixed in it would do the trick.

Apparently these devices work for central heating systems too:

http://www.scalemaster.co.uk/hcc/hcc_physical_pages/hcc_physical_home.html

cheers,
Pete.