Sealed System Additional Expansion Vessel Needed?

[cr0ft]

Hi all,

As a few of you will know, I'm a bit rusty on the tools now and was wondering how to tell whether an additional expansion vessel is needed.

In short: -

Have moved into a house with a sealed heating system, system keeps losing pressure but no obvious leaks. It's heated by a Greenstar Camray Utility System boiler running at 25KW. The house is approximately 300m2 over 3 floors and split into 2 heating zones (ground floor UFH and first/second floor).

Ground floor

12 UFH circuits off a Speedfit manifold, serving a total floor area of circa 120m2.

First floor

3 1400x600 double radiators.
2 1000x600 single panel radiators.
2 1800x600 towel rails.

Second floor

2 x 1400x600 double radiators .

The system is experiencing spikes in pressure when running so I checked the expansion vessel in the oil boiler this morning and, sure enough, the membrane has burst.

2 questions really.

1 - how do I size the vessel that's required.
2 - is there any reason I can't just remove the expansion vessel that's in the system boiler and fit one suitably sized one on the boiler flow pipework upstairs in the airing cupboard? I don't really see the point of buying another one at Worcester prices if the existing one is undersized as I'll still need to buy and fit another one.

If my memory serves the 10 litre vessel in the boiler will be half air half water, so 5L of air space for expansion = max. 125L system? 5 divided by 0.04? Would appreciate folks thoughts on this really, to me the one in the existing expansion vessel will be significantly undersized and I want to get the final solution right!

Thanks,

Keiran.

 

[ShaunCorbs]

21l roughly

1l per rad and for ufh 1l per zone

that’s fine

 

[cr0ft]

21l roughly

1l per rad and for ufh 1l per zone

that’s fine

Grand. Do double rads count as 2 rads though? If so I'd be on 26L so would want a 30L vessel? Or will 24L do in your experience? Also as long as the expansion vessel is connected onto the boiler return is there any reason why I need to replace the one in the boiler? I'd prefer just to buy one large one - the Worcester is over twice the price of a suitably sized one!

 

[SimonG]

Dont touch the Worcester ones, over priced. I would just leave the one on the boiler and add a 18 litre one on the return.

 

[ShaunCorbs]

Grand. Do double rads count as 2 rads though? If so I'd be on 26L so would want a 30L vessel? Or will 24L do in your experience? Also as long as the expansion vessel is connected onto the boiler return is there any reason why I need to replace the one in the boiler? I'd prefer just to buy one large one - the Worcester is over twice the price of a suitably sized one!

no just work it the same eg 1l

and that’s fine