Air suddenly in central heating system

[Sussexlad]

It's an open vented system and I had the old Glow worm boiler replaced with a Vaillant a couple of years ago. Following the change, there was virtually no air gathering in any of the radiators. However, for the last few months this has changed and after a couple of weeks I can bleed out a considerable amount.
My first and only thought was that it was pumping over, partly because I'm not aware of any other reason and secondly because the surface of the header tank was absolutely clear and not scummed over!

I spoke to the guy who fitted the boiler and he suggested placing a plastic bag - with a hole in the side - to see if this was the case. Well after a few more weeks, there is no evidence of water in the bag however the air is still getting in somewhere. I would have thought that air getting in would be accompanied by water getting out but there's no evidence of that, so what's happening? The boiler/system is more noisy first thing in the morning and the boiler can sound a bit like a jet engine, which I've not noticed before.

I'll have to get the guy up but are there any suggestions as to why this might be?

Cheers

[Urbandreamer]

Are you sure its "air"?

Radiators are usually steel and pipes copper, heat exchanges may be aluminium. The result, without adding an inhibiter to the water, is galvonic corrosion. The electrical current caused splits the water into H and O2 gasses. The rust flakes off and is pumped arround the system.

[Watis]

Are you sure its "air"?

Radiators are usually steel and pipes copper, heat exchanges may be aluminium. The result, without adding an inhibiter to the water, is galvonic corrosion. The electrical current caused splits the water into H and O2 gasses. The rust flakes off and is pumped arround the system.

So . . . it's inadvisable to smoke while you're bleeding radiators?

Who knew!

Watis

[Urbandreamer]

So . . . it's inadvisable to smoke while you're bleeding radiators?

Who knew!

Watis

One or two people did. Here is a video.
https://www.youtube.com/watch?v=0GXDKxX9C7E

[bungeejumper]

One or two people did. Here is a video.
https://www.youtube.com/watch?v=0GXDKxX9C7E

That is a lot of hydrogen! But I do remember that my first DIY plumbing guide encouraged me to test the escaping gases with a match - presumably so as to be sure that it wasn't hydrogen sulphide instead? (I imagine that the explosive potential of the two may be different?)

Being young and impressionable, I tried it, and it worked. Nice blue flame, as illustrated, but it didn't last long. Mind you, I did notice that the plastic around the fancy bleed valve in the linked video seemed to have suffered somewhat.

The OP will probably want to question how much inhibitor is in the system. (If any?) If it's producing a lot of gas, it's probably the primary suspect.

BJ

[Sussexlad]

The lack of inhibitor could be a possible cause and something I have had in mind to raise with him. I'm surprised though by the quantity of 'gas' within just a few days! Thanks for the suggestion.

[wilbobob]

Might you have a leak from the system so that it has been topping itself up in the header tank and reducing the level of inhibitor in the system? Tying up the ball valve and checking after a day or two should tell you

[bungeejumper]

The lack of inhibitor could be a possible cause and something I have had in mind to raise with him. I'm surprised though by the quantity of 'gas' within just a few days!

If there's a lot of gas in a system, it might take several goes to bleed it all out, so it might not necessarily be too ominous if it seems to keep on coming. The gas can hide away in airlocks and all sorts of other obscure places, and it might take a while to winkle it all out. Maybe try turning the pump up to max, and running the boiler at a high setting for a couple of hours to see if you can dislodge it?

WRT the inhibitor, I think the usual dilution is 1 litre for every 100 litres in your system, but it's actually quite hard to overdo the dosage. A very broad rule of thumb says you've got 10 litres of water for every radiator, plus a bit more for the boiler I suppose. One 1-litre bottle will do an average house, but we have 17 radiators plus a header tank, so I tend to guesstimate the dosage at two litres (200 litres in the system). Seems to work for me - I bled the radiators recently for the first time in three years, and they were completely clear of gas.

BJ

[Itsallaguess]

The boiler/system is more noisy first thing in the morning and the boiler can sound a bit like a jet engine, which I've not noticed before.

Could this be significant, given that it sounds like the increase in noise from the boiler has coincided with the need to keep releasing air from the system?

Could kettling in the boiler be the cause of both issues here?

Cheers,

Itsallaguess

[Sussexlad]

Thanks for the various suggestions, I'll be getting my man in but I wanted to have a better idea of what might be going on. It's just the amount of 'gas' which has suddenly increased noticeably. I much preferred my old basic Glow worm which I looked after myself for close on 30 years but the new one is more of a mystery!

[88V8]

Could kettling in the boiler be the cause of both issues here?

Kettling would be a consequence of no inhibitor, or insufficient.
Cheapskate installers skimp on inhibitor or omit it entirely.
That kills the boiler.

Leaks can eventually lead to a dilution, but so soon after a new boiler, I would be suspicious of the installer.

The gas is a by-product of the steel rads rusting, accelerated by galvanic action, as has been said.

The boiler is killed by scale deposit on the heat exchanger. It only needs a flash of scale, modern boilers with their alloy exchangers are not tolerant of scale as were the iron units of yore.
The heat exchanger can't lose the heat fast enough and overheats, distorts. You hear the overheating as kettling.
Inhibitor should have been in there from first firing, to prevent the scale.

Your system now needs an acid descale, which is a blooming palaver. There are descalers one can leave in the system without the umpteen flushes that make acid such a pain, but I have no experience of them.

If you do the descale now, that's now, you may not need a new boiler.
Meanwhile, turn down the boiler temperature until the kettling stops. Wear a wooly.

V8

[Sussexlad]

If the outcome was that dire, a new boiler, the current one does have a 10 year guarantee.

[sg31]

If the outcome was that dire, a new boiler, the current one does have a 10 year guarantee.

Watch the exclusion clauses. Lack of inhibitor might invalidate the boiler warranty. From memory the boiler fitting instructions specify that the system should be powerflushed before the new boiler is fiited. There might be something about inhibitor in the small print.

[bungeejumper]

Your system now needs an acid descale, which is a blooming palaver. There are descalers one can leave in the system without the umpteen flushes that make acid such a pain, but I have no experience of them.

I got mine sorted with a system cleaner, Sentinel X400, which you tip into the system and then leave for a couple of months. The bad news is that it took three (four?) full drain-downs before my inky black water had turned crystal clear; the good news is that it only cost about thirty quid for two treatments (plus two clear water flushes), and anyone with a spanner could do it. Followed up with a normal inhibitor, and my system has stayed fixed ever since. (About eight years so far, I think.)

Our system isn't typical - our boiler is a cast-iron gas Rayburn that's now 22 years old - but we were warned that a full powerflush might be more than the old monster's heat exchangers could withstand! - but all in all, it was a successful manoeuvre. The OP's Vaillant sounds more amenable.

IIRC, the reasons for powerflushing when installing a new boiler are at least partly to do with wanting to eliminate any slivers of copper, old fibre washers and other assorted crud that may have got loose during the process?

BJ