New system - think I have an air leak somewhere

[dexus]

Three month old sealed system:
Vaillant 630 system boiler (integral pump) in garage
New hot water cylinder in airing cupboard on first floor.
Vertical distance < 2 metres between cylinder flow/return connections and boiler.
New three-way valve and new above-floorboard pipework. Remaining pipework is from previous installation.

Setup in the airing cupboard in picture below.

Untitled

• dexus
• 6 Nov 2008
• 1

System has been thoroughly bled, but air is still getting in somewhere - evident gurgling noise when just the HW is on (no noise when just the CH is on or both HW and CH on together). I *think* I can hear a noise that sounds like air being drawn in or expelled in the airing cupboard when just the HW is on, but could be carried noise from elsewhere.

The air is eventually making its way to the highest radiator in the system, which I bleed out. More air can be found a few days later. I've done the upturned beaker test for hydrogen - it's not that.

I've read (and probably misunderstood) from other postings on the forum that a sealed cannot admit air if pressure is >1 bar throughout the system. The pressure gauge in the picture is always >1 bar as is the (digital) gauge on the boiler itself.

The auto-air vent (pictured top right) is screwed closed. The pump is vented, and is connected to the flow side of the boiler.

My current theory is that the negative pressure caused by the pump is causing the system to drop to < atmospheric pressure somewhere in the HW loop, dragging in air. Plausible?

Interestingly, the gurgling noise is louder after the CH goes off when CH and HW have been on together. The system pressure is greater in this scenario (~2.0 bar on the airing cupboard gauge) than when just the HW has been on by itself (~1.7 bar).


Be nice to the newbie

Thanks in advance for any help/thoughts
Dexus [/img]

 

[spacethegas]

loosen the cap on the aav & let it do its job.

 

[Bambergaspipe]

loosen the cap on the aav & let it do its job.

What he said....

 

[gas4you]

More likely each time you bleed and re-fill the system you are adding fresh oxygenated water to the system.

Sure you have no leaks anywhere?

 

[Bambergaspipe]

More likely each time you bleed and re-fill the system you are adding fresh oxygenated water to the system.

Sure you have no leaks anywhere?

That would be if he had a header tank wouldn`t it? it`s a sealed system so the oxygenated water theory doesn`t come in to it, other wise we would all be bleeding combi installations wouldn`t we?

 

[gas4you]

Every time he gets rid of the 'air' in the system he will have to re-pressurise it, so adding fresh water into the system, so the cycle starts again.

 

[dexus]

The AAV was closed recently, just to demonstrate that it wasn't the AAV that was permitting air in. It's usually open, and has had plenty of opportunity to bleed out any air in the HW circuit.

Agree that adding fresh water is bringing more air into the system, but I need to bleed the existing air out At any rate, even if I leave the air in the highest radiator, the HW still makes loud gurgling noises.

Grateful for any other insights - thanks.


Dexus