Mains water expansion vessel

From the Alpha combi boiler instructions:
"Note: If the mains is fitted with water meter, check valves or loose
jumper stop cock, then a DHW expansion device must be fitted."
and there's a similar note in the W-B Si instructions, but not in, for
instance the Glow-worm equivalents. I can see that there is a risk of
trapping a quantity of water in a length of pipe, which then gets
warmer, but doesn't this apply to all cold water systems?
Does anyone fit these devices in real life?
Reply to
Autolycus
Do you mean they are an integral part of some boilers?
Would you, Ed, fit an external one to, say, a W-B Si? They're not at item I've often seen listed.
Reply to
Autolycus
Only boilers with gas-to-DHW heat exchangers (rather than gas-to-primary and primary-to-DHW). The old W-B (non-Greenstar) iJunior was another example, as I think were some Ferrolis.
On the Juniors I fitted I didn't have water meters or loose jumpers on the stopcocks. I'd guess/hope that in any real-world installation a WC cistern valve would provide a pressure-relief path. However to be safe you can get little potable expansion vessels cheaply enough (e.g. from Toolstation)
Reply to
John Stumbles
Yes.
To fit externally is very unusual but they are available they are called shock arrestors, are more or less spherical and would fit into a 100mm cube. Nevertheless that the same as any other expansion vessel, you need a blue one for use on potable water.
I suppose I would look at the instructions carefully before fitting one to see if I really had to. Also I might change the main stop valve for a 1/4 turn full bore level valve (WRC approved) this latter being, usually, already in available in the van.
Reply to
Ed Sirett

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