Megaflo Unvented Cylinders & radiators

[Philip64]

I am converting my loft, as so many people do. In order to get rid of the water tanks currently in the roof, I've been advised to install a Megaflo-type pressirused hot water cylinder in place of my old copper cylinder. I am not replacing by old gas-fired boiler.
I am looking at a number of different models - Megaflo, Santon, Vaillant, Tribune amd possibly some others. What I remain unclear about is whether these types of tank will also serve my radiator system. If I turn my radiator system into a closed system (which I need to do); is there any additional kit I need? I have received contradictory advice on this.
As a secondary issue: does anyone have a view of which of these tanks offers the best value. I have heard people say with Megaflo (and Vaillant, annoyingly) you are paying extra for sleek looks and a brand.
Advice much appreciated!

[plumbbob]

Assuming the existing boiler is suitable for an unvented system and the radiators and pipe work are in good condition then converting the system should be fine, The heating will work in the same way as it does now.

As for the difference in prices? Well the phrase "buy cheap, buy twice" stands up well. When you see branded and unbranded boilers side by side the difference becomes obvious. Certainly, brands will pay more attention to design, but there will be other less obvious differences too. Far better to make a decision according to what you are prepared to spend rather than simply heading straight for the cheapest option.

[Philip64]

Many thanks PlumBob. My existing boiler is a Kingfisher II. My radiators look ok, but I plan to replace some of the valves once the system is drained. I have the option of maintaining the header tank, but I'm not sure if it will be high enough above the top floor radiator(s) to work well. I think the most height we could get would be roughly 1.25m. And it probably couldn't be directly above the radiator, would take up space, look ugly etc...

I'm hoping a sealed system will not have me springing leaks all over the place. Is the additional pressure very great?

[plumbbob]

The Kingfisher ought to handle the pressure ok and so should most heating systems. It is only very old installations with extreme corrosion or those using sub-standard materials that might suffer from leaks.

The pressure in a sealed system will be somewhere between 1.0, and 2.0 bar (a head of between 10 and 20 metres).