Vaillant Ecotec 418 in a sealed system

Hi all,

Complete plumbing novice here, so please be gentle.

We have a sealed CH system, and recently had our boiler, hot water tank and pump replaced. Since then we've had the devil of a time getting air out of the system; it constantly finds its way to the boiler, which then races to boiling point, does a passable impression of a B-52 dropping cymbals on a tin roof, and switches off.

Today we noticed that the boiler that has been installed is an Ecotec Plus 418, which Vaillant describe as an open vent model. A quick search of these forums leads me to believe that these can be used in a sealed system, but only with "the right equipment".

Can anyone explain what equipment this might be? It seems to me that you'd need an automatic air vent very near the boiler, this being the main thing the 618 seems to have that the 418 doesn't. I can't see any such vent in evidence. There's a couple of regular bleed valves just above the boiler, but they're not automatic, and they have hardly any space to trap air. Are there any other things that would make it obvious an open vent boiler has been wrongly used in a closed vent system?

Any help will be greatly appreciated - I'd rather not accuse the installer of being an eejit without just cause...

DB

it is fine to a 418 on a sealed system, a sealed system shouldn;t be collecting any air in at all.

the right equipment, means a fill loop to BS, an expansion vessel sized to system, a pressure relief valve, and a pressure guage.

Automatic air vents shouldn;t be necessary, on a sealed system.

Thanks for the reply, spike, much appreciated. It's not so much collecting air, though, as much as it's never been completely filled. The plumber himself says he can't see how the people who put our system in in the first place ever got it filled, given the layout, which involves a looong run of pipe between boiler and tank, above both:

[code:1] bleed v.
^
|
=============================================
|| ||
|| ||
|| ||
|| ||
BOILER ||
||
TANK[/code:1]

We keep getting thimblefuls of air out of the bleed valves above the boiler, but not enough to make you think the system is ever actually air-free.

Ta also for the automatic vent info - the FAQ on this site specifically mentions them regarding bleeding sealed systems, and all of Vaillant's sealed system boilers seem to have one, so I'd assumed they had to be there. Is it that they're a "nice to have, but not essential" thing?

On a sealed system, then you should be able to have a long horiziontial run, I;d take the pressure upto about 2bar, to compress the air, bled again from those high air vents.

It may be, gassing, with can be caused by a dirty system, so gas is being created.

Every combi/system boiler has an auto air vent, I guess its manufactures way of ensuring air is cleared from the heat exchanger. I dont like them as can mask a problem, and often leak after time.

Okay, thanks very much Spike. Will return to bleeding and swearing at the god of plumbing.