Unvented cylinder -Internal or external pressure vessel?

[xyz123]

Hi, we are having our boiler replaced with system boiler and unvented cylinder. Plumber has proposed Main brand cylinder which has external pressure vessel. I know there are some which have internal vassel as well. Is either one (internal or external) better than the other? Any feedback on Main brand cylinders?

Thanks

[21TonyK]

I've had several over the years, in use, no difference and the OSO ones which were internal (I had 3) were all fine for 8-10 years before we moved. Subsequent ones have been external and aside from the space, no issues. Only thing would be if the vessel did fail then obviously its easily replaced.

[Fore Left]

External. Having to repressurise my Megaflo every few months is a right pita.

[netherfield]

Yes I'd say outside as well, we had to have one replaced, did 5 or 6 years before the cylinder leaked.

[GasEngineer]

External expansion vessel is definitely easier to maintain, plus you get a higher capacity cylinder for the same external measurements as it is full of water not part air.

There is nothing to choose between cylinders. They are all exactly the same construction and insulation with usually 25 year warranty. Just look for the best price.

[Huzzah]

Ours failed so plumber fitted an expansion vessel. Fortunately plenty of space.

[xyz123]

Thanks everyone.