What is this small White Vessel next to Worcester Boiler?

FrankFalcon

Hi all

My daughter has just got her first house. We had a tour round the house last night and saw this (small White cylindrical vessel) at the side of the boiler (Worcester Greenstar i). What is this please? What is the purpose of this? Is it actually in use given that the boiler is surely a combi?

Thanks in advance. 

bazdvd

Expansion Vessel

https://www.vaillant.co.uk/advice/understanding-heating-technology/boilers/what-is-an-expansion-vessel/

FrankFalcon

Thank you. For the reply. I understand it now. It’s just that I’ve never seen one with a combi previously. All makes sense now. 

Cheers 

FreeBear

Are you sure it is a combi boiler ?

Most (all ?) expansion vessels for a combi boiler are internal as are a lot of system & heat only boilers. If there is an unvented DHW cylinder, that would explain an external EV.

jefaz07

FreeBear said:

Are you sure it is a combi boiler ?

Most (all ?) expansion vessels for a combi boiler are internal as are a lot of system & heat only boilers. If there is an unvented DHW cylinder, that would explain an external EV.

Looks like a combi. Has a HW expansion vessel and TF1 on the return. This is an educated guess as you can’t see the other 2 pipes. A white expansion vessel is for potable water, the ones built into a boiler will be for heating. Possibly had an unvented tank before as there is a reducing set and PRV on the cold feed. 

ThisIsWeird

It's connected to a pressure release valve, so must be an expansion vessel for some purpose. Yes, that boiler (if combi) should have one inside it, but perhaps it's failed?

FrankF, any idea where these chrome pipes go to - could you trace them and report back?

Grenage

It's not uncommon for replacement expansion vessels to be placed outside the boiler.

rob7475

On older WB boilers, the expansion vessel slid upwards out of the back which made it a nightmare to replace. When ours failed, I replaced it with an external expansion vessel as the only other option was to remove the boiler from the wall to get to the EV.

ComicGeek

It's also not uncommon for an additional expansion vessel to be needed, as the integral expansion vessels in combi boilers are normally only sized for small flats. 

jefaz07

But this is a potable water expansion vessel on the cold feed. Not part of the heating system. It would be red and normally on the boiler return if part of the heating system. 

ThisIsWeird

What's the difference between the two types, I wonder? Apart from colour...
The white one uses non-toxic materials, I guess? But could it otherwise be used on a 'system'?