Why Do Cold Feeds Get Blocked?

[CareerChangeChancer]

Was wondering the other day, why it is that cold feeds block with magnetite in that location? What is it about the tee and its position that attracts the magnetite build up?

Why doesn't the magnetite cause regular blockages in other places/tees?

 

[misterdubya]

Because its a neutral pressure point. No circulation is occuring at where it blocks up is it? It can happen to the open vent too - even when its 22mm.

Had a 28mm c/f blocked once, but that was on 42mm primaries. Is that a record?

Are you planning to become a plumber?

Mr. W.

 

[Onetap]

Was wondering the other day, why it is that cold feeds block with magnetite in that location? What is it about the tee and its position that attracts the magnetite build up?

Why doesn't the magnetite cause regular blockages in other places/tees?

Because there is a leak and it is the point at which the cold feed water enters the hot heating system. The solubility of limescale (calcium carbonate/bicarbonate) is less in hot water, so the excess limescale drops out of solution at the point where the water is first heated, i.e. the cold feed connection.

The blockage is limescale that is blackened by magnetite. You can dissolve it with acid descaling solution which won't touch magnetite. It's easiest to cut out the blocked connection.

 

[Agile]

I think that you will find that its a complex calcium/iron carbonate. [ CaFe(CO3)2 ]

Its very hard and little affected by the acids used on heating systems although it dissolves well in HCl.

As said best to cut out the blocked pipes and unblock or replace and refit with compression couplers.

It also readily blocks plate heat exchangers where water of moderate hardness is supplied from cast iron pipes and a fault causes a small flow of cold through the plate HE during heating mode when the temperature is around 80C. When dissolved in HCl it bubbles a lot and produces a brown effluent.

Tony