Auto Air Bleed Valve

[John]

(I had no response to earlier note - Worcester Highflow!)

I was getting a lot of air gurgling around in my system despite bleeding the rads every day.

Took a look at the boiler - it has an auto bleed valve. Poked a blunt pin into the hole and must have dislodged some crust of something - air came out for about 5 minutes - now the valve seems to be weeping water.

Might it recover - how do they work?

[Andy Hall]

It may seal up with crud again but I wouldn't count on it. Often valves like this or pressure relief valves build up a deposit or are subject to some corrosion.

Most AAVs have a chamber with a float - rather like a tiny toilet cistern without the flush. When air finds its way into the chamber, the water is displaced and the float drops, opening a vent. When the water comes in the float covers the vent hole.

Some of them can be taken apart for cleaning, it depends on the type. Either way it will be a drain down job and either clean or replace.

.andy

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[IMM]

Some can be taken off the system without a drain down.

[Andy Hall]

Yes, you're right, I realised that after I had posted - I have some of them so I should know.....

The Honeywell ones, for example. have a second valve in the base which closes as the body is unscrewed.

Whether that type would be fitted inside a boiler, I'm not sure, though....

.andy

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[IMM]

[John]

Thanks for your help - is it likely that I have punctured the float?

I will be looking for a replacement tomorrow. In the meantime the toothpaste tube cap is keeping things dry.

[Andy Hall]

It could be, or simply the vent. Generally there is a little rubber cap which covers the hole on the inside. It could simply be that you've scratched that.

.andy

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[Dave Liquorice]

I wouldn't have thought so, gets rather hot inside a boiler casing. The air valve on our (38KW Oil) boiler is of the fibre washer type. Can I find one on the web? Nope, they are similar to:

that the just below the thumb screw is a ring of holes, through which you can see a fibre washer. When the washer dries out it shrinks letting out the air, it gets wet expands and seals simple and effective.

[John]

I took the old valve apart - it is like a small ball valve - the float (through linkages) presses a rubber nipple onto a small seating. As with a ball valve, the rubber had pitted a bit (probably helped by my probing with a pin!)