Sealed system continually grabbing air

[Matt887]

What can caused a sealed C/H system to constantly keep grabbing air in the upstairs airs? The auto air vent on the boiler sucking air in? Sludge in the system creating air? Anything else. Thanka

 

[ianmcd]

first thing is to confirm it is actually air, could be hydrogen forming and the system needs treated

 

[Matt887]

Thanks. Bar igniting the gas is there a way of checking if it's hydrogen?

 

[John D v2.0]

Not enough water in the system for the cold volume, and there's a leak that can let in air somewhere?
Check the charge pressure of the expansion vessel is lower than the cold pressure, and that the cold pressure is enough to fill the highest part of the system with the pump and valves in all positions.

 

[Matt887]

Thanks it's a sealed system combi Worcester Bosch boiler. Though it was converted from an open vented system before the boiler was installed

 

[Johntheo5]

Is it a fully sealed system with a top up (valves) from the mains to give 1.3 to 1.5 bar when cold?. some of these systems are semi sealed where a non return valve is installed in the cold feed from the existing feed & expansion tank and the vent is blanked off, the cold pressure will then only be 0.4/0.5 bar. If the former, ensure cold pressure allways > 1.0 bar.

 

[fixitflav]

Thanks. Bar igniting the gas is there a way of checking if it's hydrogen?

No easy way I know of. Does it burn?

 

[RayCaister]

No easy way I know of. Does it burn?

 

[fixitflav]

View attachment 295183

But we're not talking about a Zeppelin-full! Any risk from lighting it was discussed on here a few weeks back.

 

[45yearsagasman]

Hold a container (small tin can?) inverted over the bleed screw and collect the gas that comes out. Still holding the container upside down, try lighting the contents.

 

[fixitflav]

Here's the link

Central heating - Air not gases replaces water but the pressure doesn’t drop

I have changed the title to dismiss gas causing the problem. I can understand that if there is a weep on a sealed system then the boiler gauge pressure will eventually show a drop. On my combi the pressure gauge doesn’t move and stays constant until I bleed a towel rail. Then the pressure gauge...

www.diynot.com

 

[Johntheo5]

If you get AIR ingress in a sealed system surely the pressure will rise once the air heats up??.

 

[John D v2.0]

If you get AIR ingress in a sealed system surely the pressure will rise once the air heats up??.

Yes, the pressure also rises when the (incompressible) water heats up, hence the need for an expansion vessel

 

[Johntheo5]

Thats not quite what I meant, if you have a system with say pre and filling pressures of 1.0/1.5 bar and the system rises normally to say 2.0 bar on heating up, then with air ingress the pressure might then rise to 2.1/2.2 bar but then return to 2.0 bar when the air is vented.

 

[John D v2.0]

Yes that's true but that would apply to the cold pressure as well so isn't specifically related to the heating up