Air in Heating System - Opinions please

[ne0]

Background

Had a radiator installed in living room last year - plumber had trouble getting the new join to seal properly (not sure why...) which meant quite a few attempts of refilling the system to check for leaks, etc.

During this work, the auto air vent in the boiler starting leaking a lot of water so the plumber closed it off and called it a day. I assume it got some crud in it and prevented it from closing.

Now, I know from my own research that there's a bit of a debate about whether these should be left open or closed, but it makes sense to me that they should be left open otherwise they can't do their job.

I was concerned, so I had a boiler service done shortly after and asked the guy to check the AAV. He told me he checked it and it was fine and gave me the impression he had left it open.

Fast forward to this winter and I've noticed a few issues:

• 1 of the radiators upstairs keeps getting air in it meaning I'm having to bleed it once a week. After bleeding the rad, the pressure drops so I'm having to open the filling loop for a few seconds to top it up a bit.
• There's a whistling noise coming from the boiler.
• Today I decided to check the AAV in the boiler was actually open as the previous fella had told me and low and behold it was fully closed! I opened it just a tad and it started leaking water.

I'm assuming this means I need to get the AAV replaced which I will do, however, I'm trying to understand if I have a bigger problem with having to keep bleeding the radiator or is this all linked to the dodgy AAV?

I've checked all around the area where the original plumber had problems sealing the joint when installing the rad (it is buried in the wall) but I can't see or feel any signs of damp.
I also made sure to leave that joint exposed for at least a week before having it boarded over as I was paranoid about it leaking but it was dry as the Sahara.

I should also point out that for a while after having the rad moved I kept checking the boiler pressure as was worried about leaks and it was solid throughout the whole of summer/autumn - it's only since we've been using the heating this winter that the problems have started.

Any advice, thoughts welcome.

Thanks.

 

[Mekrel]

Sounds to me as if you have air build up not from a leak, but perhaps from corrosion within the system? If the system has none or too little corrosion inhibitor in, you'll have corrosion taking place which will create gas when that reaction takes place.

Do you have a magnacleanse on the cold return to the boiler?

 

[ne0]

Sounds to me as if you have air build up not from a leak, but perhaps from corrosion within the system? If the system has none or too little corrosion inhibitor in, you'll have corrosion taking place which will create gas when that reaction takes place.

Do you have a magnacleanse on the cold return to the boiler?

Thanks.

I added inhibitor in the summer so thought I should be covered in that area. But the radiator in question does have signs of corrosion (green stuff) around the lock shield valve albeit no detectable leak. Is that something to do with it?

I don't have magnacleanse.

 

[shroomz]

It does sound like the AAV got blocked open and if pressure drops it can suck in air if it's not properly operating. Do you have a ball valve upstream of the AAV you could close to change it? They're not expensive to replace or complicated diy if you can isolate

 

[shroomz]

Green stuff on the outside is not necessary a problem, that's copper oxidising. corrosion inhibitor is a good point since it keeps recurring. Drain a bit of the internal water and does it have and black sediment?

 

[FlyingFish]

It's relatively easy and straight forward to swap an AAV inside most modern boilers. So it shouldn't cost much to get a professional in to sort this out for you, most are bayonet fitting or clip.

An inbuilt (inside boiler) AAV cannot introduce air into a system, even when faulty. The only way, would be if the system is being drained from a level lower than the boiler, or there is a leak so bad below the boiler that it's draining not only the pressure but the volume of water away, and air is needed to allow the water to drain.

If there is an AAV fitted externally to the boiler, then these can under rare circumstances introduce air, but that would only happen with zero water pressure (not quantity) and the AAV installed on the negative side of the pump. But that would be poor plumbing/installation.

Excessive air generated by a working system is either down to poor circulation, scaled up gas to water heat exchanger, or boiler temperature/output (kw) too high for system design/capability. Imagine a pan of water heated on the hob, and all the microscopic air bubbles created...Same principle inside a boiler, except those air bubbles are pumped from the flow side, and most boilers have their AAV on the pump housing, on the return...That's why air gets trapped in a radiator, and not vented by the boiler.

 

[ne0]

It's relatively easy and straight forward to swap an AAV inside most modern boilers. So it shouldn't cost much to get a professional in to sort this out for you, most are bayonet fitting or clip.

An inbuilt (inside boiler) AAV cannot introduce air into a system, even when faulty. The only way, would be if the system is being drained from a level lower than the boiler, or there is a leak so bad below the boiler that it's draining not only the pressure but the volume of water away, and air is needed to allow the water to drain.

If there is an AAV fitted externally to the boiler, then these can under rare circumstances introduce air, but that would only happen with zero water pressure (not quantity) and the AAV installed on the negative side of the pump. But that would be poor plumbing/installation.

Excessive air generated by a working system is either down to poor circulation, scaled up gas to water heat exchanger, or boiler temperature/output (kw) too high for system design/capability. Imagine a pan of water heated on the hob, and all the microscopic air bubbles created...Same principle inside a boiler, except those air bubbles are pumped from the flow side, and most boilers have their AAV on the pump housing, on the return...That's why air gets trapped in a radiator, and not vented by the boiler.

When you say poor circulation; could this be due to me attempting to balance the radiators at the beginning of winter? I've been messing with the lock shield valves.

The temperature is currently set to 80c which I know is on the high side. Will double check what it should be set to for my boiler.

 

[ne0]

Green stuff on the outside is not necessary a problem, that's copper oxidising. corrosion inhibitor is a good point since it keeps recurring. Drain a bit of the internal water and does it have and black sediment?

Nope, water is clear.

 

[ne0]

It does sound like the AAV got blocked open and if pressure drops it can suck in air if it's not properly operating. Do you have a ball valve upstream of the AAV you could close to change it? They're not expensive to replace or complicated diy if you can isolate

Not sure but wouldn't be doing it myself anyway, not my area of expertise