Filling Loop

[Best]

Flamco auto fill kit is available from Plumb Centre but I am sure it would be cheaper just to buy a 15mm PRV.
Make sure you do not over pressurise a new heating system on initial fill, as the expansion vessels corrode quickly, I discovered (despite inhibitor added) & I can only assume this is the reason. They seem to not corrode if system, when it is being filled, is not taken much above the needed final cold fill.

 

[DirksPlumbing]

Flamco auto fill kit is available from Plumb Centre but I am sure it would be cheaper just to buy a 15mm PRV.
Make sure you do not over pressurise a new heating system on initial fill, as the expansion vessels corrode quickly, I discovered (despite inhibitor added) & I can only assume this is the reason. They seem to not corrode if system, when it is being filled, is not taken much above the needed final cold fill.

If on the initial fill some water containing flux would get deep into the vessel it would most likely not get flushed out completely afterwards and could cause this kind of issues.
Gap corrosion is a problem in itself but with trapped chemicals like flux this could cause rapid corrosion indeed.

 

[Best]

If on the initial fill some water containing flux would get deep into the vessel it would most likely not get flushed out completely afterwards and could cause this kind of issues.
Gap corrosion is a problem in itself but with trapped chemicals like flux this could cause rapid corrosion indeed.

I cut one of the corroded expansion vessels open using an angle grinder & there was some rusting near the middle of the inside of vessel, close to the edge of diaphragm. Only theory I could think of was that it was the fresh water, not yet mixed with inhibitor, & with oxygen trapped between side of vessel & edge of diaphragm, causing this, if that is possible. A replacement vessel seems to last & last.
Perhaps flux is a factor, although I personally use only grease based Yorkshire traditional flux or Fluxite, which should be fairly mild.
Guess it is best to both not over pressure initially the system plus flush it well (& use less harmful fluxes).