On Mon, 09 Jan 2006 15:48:44 +0000, sPoNiX wrote:

On Mon, 09 Jan 2006 14:38:08 +0000, Andy Hall
wrote:

You wouldn't expect to find scale in the cold water pipes. If you
think about it, if that were to happen, all the street mains would be
in severe trouble by now. The calcium and magnesium compounds in
scale come out of solution on heating and generally on the heating
surfaces, so you would expect to find it on the surfaces of the coil
inside the HW cylinder and possibly inside some of the pipes in the
near vicinity. On older systems with a direct cylinder where there
is no coil and the DHW circulates by convection through the boiler,
you would expect to find scaling of the boiler and pipework from it.

The water in the heating circuit seldom changes, so no significant
scaling there. If the system doesn't have problems with pumping over
or sucking down because of pump placement and pipework, then initial
dissolved oxygen, causing corrosion would be used up.

You might find that if you check the radiators, there is more
magnetite in these since the water is crossing radiators at a lower
speed at a given point than it will be through the pipes feeding them.
Hence material is deposited, typically in a triangular shape at the
bottom.

I'll check the cylinder when it comes out and see if it's more scaley.

An inch or two of flakey stuff is quite common after 20 years.


--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html