Changing the AAV

[richie4236]

Recently drained and refilled our open vented system with X400 to clean it out. It's been a long time since it was done. It went well. I carefully filled and then vented all the rads, but there's clearly air in the system.

What I think is happening, is this:

At the very top of our system (crown?) are two vertical 22mm pipes and a dome shaped AAV. From the top of the AAV, a pipe leads up and bends over the F&E tank, with about 30cm of extra height above the tank fill level. When the pump runs the rads get hot, and when the pump stops, I can clearly hear air rushing up the pipes, past the pump and into the U of pipe where the AAV lives. The fact this happens suggests to me the AAV isn't working, and that trapped air gets pushed down when the pump runs, then returns to the highest possible point in the system when it's off.

The rad on the landing - which I'm guessing is the very first one off the manifold, given it's location - gets a lot of air and has to be bled often, so presumably, the air gets pushed here first, but not all of it. Also explains why that rad makes a lot of noise when the pump starts. It's the air being pushed into it, bubbling in the rad, as it's forced down by water pressure.

The HTW is close to the pump too, and I wonder if some of that air is getting forced into the coil, making it inefficient; and explaining why our hot water is mostly tepid.

There's no manual vent anywhere near the AAV, on the tank feed, or the pump, making the landing rad the closest I can get to bleed air from the top of the system.

My plan is this:

Cut the two 22mm pipes below the AAV, and cut the pipe that leads up from it. Fabricate a replacement with compression joints that can slide over the two parallel pipes, with a T that leads upwards, and joins the pipe over the F&E tank.

But, where does the new AAV go in this configuration, and what's the best one I can buy?

 

[cross thread]

Put photos on showing your existing setup.correctly piped it should not have the issues you are describing.

 

[Johntheo5]

??? something like one of these.

Is the pump downstream of the deaerator?

 

[richie4236]

This is on the LHS of our airing cupboard on the first floor. It's about 30cm below the ceiling, and is the highest point in the system.

1) From the boiler.
2) To the vent above the F&E tank in the loft.
3) To the pump. About 30 cm down the pipe.
4) From the F&E tank in the loft.

Circulation is clockwise in this, so the AAV is upstream of the pump, which I gather is a bad thing.

Was installed around 1990 using cheap parts. Boiler and pump have been replaced in the last ten years. Everything else original as far as I know.

 

[cross thread]

After checking your pump settings are correct I would cut that “airjack” and alter to a close couple set up easy to alter.

 

[Exedon]

As above get rid of that aerjec and repipe to H section.
They are the work of the devil try sticking a magnet on pipework near it.

 

[richie4236]

Just so I'm clear, we're talking about this when we say "H section"?

Vent goes up to above the F&E tank and bends over, so air gets out there, and so does any water if there's a problem? Fill comes after the vent, but before the pump? Am I getting it?

 

[Johntheo5]

That looks pretty like it to me, with Vent & Fill no more than 150mm apart.

 

[richie4236]

The space is a bit limited and I don't really want to do the whole airing cupboard. Would this work if I made it out of a couple of 22mm Ts, a short length to get the crossbar spaced properly, and a 15mm reducer for the fill? Distance from return to flow pipe-centres is about 5cm.

 

[Johntheo5]

As one lager seller famously says, probably, its a true H.

But I've seen cases where that very accepted close coupled setup still gave problems with pump over/air ingress even after all new pipework like yours was installed, no idea why, and was only cured by converting exactly to my over 50 year old system with some rads > 40 years old., its the combined vent and cold feed but combined high up just at the F&E cistern,

 

[Exedon]

its the combined vent and cold feed but combined high up just at the F&E cistern,

Have to say while that's obviously fine on your system its certainly not a universal cure.
I've seen many system with that arrangement some are very clean others some of dirtiest systems you have seen.
I've seen the tee blocked with debris.
Also notorious slow refilling system.