AAV Passing

[the_ace]

My sister called me saying that her boiler was losing pressure over the course of a few weeks. I went for a look and found an AAV on the C/H return into the boiler. It was passing so i checked the manufacturers instructions and found that the boiler (ideal isar) has its own AAV.

I shut the external AAV completely which stopped it passing but wondered why the installer fitted it in the first place.

Is it worth me replacing the valve or just leave it closed and use it manually?

 

[migoplumber]

you need to replace the valve


shaun

 

[the_ace]

What is the purpose of having an extra one? Surely the one in the boiler is sufficient? I would like to know the theory behind it as we didn't go into these in great detail at college.

 

[Bernie2]

Basically I suppose a quick answer would be. Many installers put air bleeds in the top of the pipework, simply because that is where air collects in a system.

The one the manufacturer puts on the boiler is to ensure any air escapes from the boiler pipework not the system pipework. That is up to the installer, where he or she puts them and where they put them is up to the design of the system, not the boiler.

An AAV just lets the air out by itself instead of having to do it by hand.

Air entrains either through system leaks, plastic pipe or its already in the water.

One old trick to prove the theory,was to get your missus stocking and hold it to your face then breath through it. Then lay it over a basin and pour water on top of it. You found you could breath through it but the water would not go through it. Same thing happens to valve glands and plastic pipe. Although they now dip some plastic pipes in resin to fill the holes up and seem to call it double barrier pipe.

Heating releases the air and it looks for somewhere to go, as it does a runner it rises and usually goes to the top of the pipework or boiler and that is why they usually stick an aav at the top of the system.

It usually gets stuck in the top of the U if your system pipework or fittings have a part that forms an inverted U shape anywhere.

If you design heating pipes with a slight rise on and then put your aav on the top of the rise that is usually enough to avoid air problems as best you can.

 

[the_ace]

Thanks for the reply Bernie2, i will take a pic of the AAV in question as it sits horizontally and i would have thought they would need to be upright in order to work properly.