Sealed v Open Vent ?

[flynot]

I wish to change my old Radiation boiler to a new Vaillant System boiler (not a combi)

Can someone please explain the difference between the "sealed" and "open vent" systems on offer. And are there any advantages or disadvantages over either .

My present system has 7 rads, a combined hot and cold tank and a small water tank for the central heating, cold water is a direct mains feed.

Regards

Peter

 

[kevindgas]

look on vaillants UK website
the 400 series are compact heat only boilers fan be open or sealed system.
the 600 series are system boilers (pump inside) same size as the 800 series combi's (same unit without the water section) these can only be on a sealed system.

 

[kevplumb]

View media item 15390
open vent system

sealed system has no header tank you have an expansion vessel and prv as well as a fill loop to pressure the system

 

[flynot]

Thanks for the replies and I can see the differences, the system I have now is open vent.

But no one has mentioned which is the better,

"Open" or "Sealed" and or why

Regards

 

[kevplumb]

sealed is generally considered better as there is no exposure of the water to the air

so "in theory" less chance of corrosion

 

[kevindgas]

open is good if you suspect the pipework won't take the pressure but otherwise a sealed system wins hands down.

 

[bengasman]

Sealed systems have several advantages.
No airlocks.
Less corrosion.
Slightly better heat transfer, at least theoretically.