Expansion vessel

[plumbane]

I have recently bought a Triton thermostatic bath/shower mixer to replace my existing bath taps; I intend to run this off my combi boiler. The blurb that came with the mixer says that an expansion vessel should be fitted to avoid damage to the mixer unit.
What does the expansion vessel do?
Where would I have to fit it?
Where can I buy one?
Any advice would be greatly appreciated.

 

[kevplumb]

takes up the expansion (names a giveaway)
on the hot water pipe
plumbers merchants

 

[croydoncorgi]

That's interesting!
What they're referring to is an expansion vessel in the HW side of the system, not the CH side. Some combi boilers include these anyway (eg. some Pumas). because with a combi there's no hot water storage, all you need is a (very small) vessel to take up possible thermal expansion of the water in the pipes between boiler and taps. The ones fitted in boilers are about 250 - 500 ml capacity. The ones for sealed CH systems and unvented HW cylinders would be far too big for your needs.

 

[plumbane]

That's interesting!
What they're referring to is an expansion vessel in the HW side of the system, not the CH side. Some combi boilers include these anyway (eg. some Pumas). because with a combi there's no hot water storage, all you need is a (very small) vessel to take up possible thermal expansion of the water in the pipes between boiler and taps. The ones fitted in boilers are about 250 - 500 ml capacity. The ones for sealed CH systems and unvented HW cylinders would be far too big for your needs.

Thanks for the reply. Looking at the manual for my boiler (Ideal isar), it shows an inbuilt expansion vessel. Presumably this serves both the CH and DHW??

 

[oilman]

Thanks for the reply. Looking at the manual for my boiler (Ideal isar), it shows an inbuilt expansion vessel. Presumably this serves both the CH and DHW??

I hope not, otherwise you could be getting corrosion inhibitor out of your hot taps. The DHW and CH should never mix. The expansion on the DHW is so small, it is usually ignored.

 

[ChrisR]

Some combis are insisting they're fitted now, in all practical situations. These are commonly used:

BES item 11355
The usual place the expansion goes is through the ball valve on a wc or other cistern. But if you have effective check valves on the mains and no cisterns, you will blow the seals on your mixer. Pipes do not accommodate expansion of water at all, contrary to lots of Manufacturers' instructions "information" you might see.

 

[plumbane]

Some combis are insisting they're fitted now, in all practical situations. These are commonly used:

BES item 11355
The usual place the expansion goes is through the ball valve on a wc or other cistern. But if you have effective check valves on the mains and no cisterns, you will blow the seals on your mixer. Pipes do not accommodate expansion of water at all, contrary to lots of Manufacturers' instructions "information" you might see.

So if I have no non-return valves fitted and a toilet on the same cold water circuit as the mixer then I should be OK