Follow-up question on Slow Leak in C/H system

[Chris Hogg]

I've now located the leak. It's on one of a pair of automatic air-vents. Easily fixed by replacement, if a bit of a fiddle, requiring partial drainage of the system etc.

But I'm wondering if they're really necessary in my situation. When the c/h system was installed in the bungalow, some twenty + years ago, the air-vents were at the highest point in the system, where they should be. But we've since had a dormer room put in, with a radiator, which means the top of the radiator is now the highest point, and I bleed that radiator once or twice over the winter months to vent trapper air.

So is there still a need for automatic air-vents that are no longer at the highest point in the system? I've a mind just to cap off the stub pipes with stop-ends and be done with it. Would that cause problems? The boiler is a Vaillant ECOmax VU226E, which AIUI has its own internal automatic air-vent anyway.

[Bob Minchin]

I'd be tempted to cap them off but with a manual bleed screw which even if only used during refilling, leaves you some options.

[fred]

In article , Chris Hogg writes

In your place I would keep at least one but possibly relocate it to either near the boiler at a natural trap point[1] or at a high (but not hidden) location. It's a handy thing to have when you are re-filling a system and can minimise your work elsewhere.

You can close the cap on top of the vent after commissioning if you are wary of leaks. If you intend to leave it open I would advise placing it in a location where you will see any leak easily

On most designs you can remove the AAV bottle for servicing without a major leak as they have a spring loaded valve seat that will close when the bottle is removed. Be prepared to lose some fluid and rapidly replace the bottle if the valve seat doesn't cut off fully. You turn just the bottle body and hold the fitting nut under it still.

[1] perhaps where a vertical run turns horizontal, change an elbow for a T and continue a stub in the vertical for 6" or so and put the AAV at the top of that.

[Tim+]

I've just had a boiler breakdown thanks to an automatic bleed valve situated above the boiler (which Is in the loft) leaking and dribbling water all over the circuit boards. Bloody awful devices! I've now fitted a stopcock to seal the system after bleeding to ensure it never happens again.

Tim

[Andrew Gabriel]

Automatic air vents will fail if left open. Normally you should open them for a day or so after refilling the system, and after that, only momentarily if necessary to bleed that bit of pipework. If left open, scale will form around the ball seal, and it will stop the seal working.

They would be installed in the highest point of a loop in the pipework, not necessarily in the highest point of the system. It depends how the pipework was changed if they are still in the right place.

[Tim+]

I wish any of the plumbers who had fitted them in my house had known or said this! It doesn't seem to be common knowledge. I only discovered that my auto vent could be closed after it had leaked into all the electrics of my boiler.

Tim

[Andrew Gabriel]

Well, I don't know if there is a type which can be left open (would be useful), but the design of the common type where a wet ball seals are bound to fail when the ball inevitably gets dirty. Closing the air vent cap prevents evaporation from the ball seal.

Plumbers often don't know the consequences of their actions unless they happen within a short length of time. Lubricating sealing surfaces of compression fittings would come top of the list - takes 1-5 years before the lubricant is forced out and starts leaking, all for the sake of getting the fitting to seal long enough to leave the premises. Seen this so many times. Properly constructed plumbing should last a minimum of 25 years before any problems appear (and a good quality installation will last much longer than that).

[Chris Hogg]

Thanks for the replies. I hadn't thought about their usefulness when refilling the system. As there are two AAV's, one on the flow, one on the return, and as it's only the one on the flow that's leaking, I'll just cap off that one and leave the other for filling purposes, to be replaced at sometime in the future if necessary.