Additional expansion vessel for Valliant ecoTEC Plus 624?

[charleston]

I had a Valliant ecoTEC Plus 624 fitted earlier in the year. The Vaillant manual says that the internal expansion vessel is suitable for a CH capacity of up to 100 litres. Using the various guides on the web I think that my CH capacity is nearer to 200 litres or a bit over (15 very large old unfinned radiators plus some bathroom towel-rails).

Is this likely to be a problem? I'm a little concerned that if anything goes wrong Vaillant will look for any warranty get-outs. I've left a phone message with the installer but thought I'd ask for opinions on here as a back-up.

Thanks.

 

[ScottishGasMan]

First off, they wont look to get out of fixing anything. If something has been installed incorrectly then they cant be expected to repair repeat failures caused by incorrect fitting.

Ideally by the sounds of it you should have a bigger expansion vessel, its not so easy to calculate the volume on older rads without the correct literature but as an estimation you would be right in saying the system is probably of a bigger than ideal volume for the built in vessel.

You cant really go wrong over sizing a vessel, but you can have a lot of bother going undersized with one. There relatively cheap items, so I would personally always err on the side of caution and fit an larger external one 15-20litres would probably be fine.

eg:
http://www.screwfix.com/p/expansion-vessel-18ltr/26891