Gassing in CH won't go away.

Turn all the rads that don't bubble off and open the ones that do fully, both end.

Best to try it individually but that could take a while.

I'm suggesting you blast each rad to purge any gunk in them, I'm assuming it's not a one pipe system

Thanks doitall, but that's just what was done during the flushing stage a few months ago.

I must now presume there is residual magnetite etc that will always remain.

Looks like Spiotech's air remover could be a last resort, but I'll wait a further couple of months.

I was thinking if there is air trapped an low spots etc then it may push it out, must be worth a try, as you said it's a large system.

Magnetite is a product of corrosion, have you tried a match to see whether the air ignites

doitall said:

The hydrogen is produced by corrosion and will smell very strong (rotten eggs is a good likeness)

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Sorry DIA, but you are wrong. Hydrogen (H) is completely odourless; it's Hydrogen Sulphide (H2S) which smells of rotten eggs.

I can't think of any way H2S would be produced in a heating system.

http://www.telegraph.co.uk/property...e-Is-my-central-heating-system-corroding.html

Jeff Howell gives it to you straight
Q.

I always keep an anti-corrosion liquid such as Fernox in my central-heating system. Last year I had to drain the system for some alterations to the pipework, so I took the opportunity to clean out the system with a de-scaler. It was then flushed thoroughly and re-filled with anti-corrosion treatment. I have noticed now, whenever I need to bleed a radiator to remove any air, that the water which comes out is black. Does this indicate a problem and what might be the cause please? CO, by email
A.

The "system" water in a central heating circuit is locked in, and can circulate around this closed network of boiler, radiators, pipes and hot-water cylinder for years without being disturbed. There will always be a small amount of corrosion taking place inside the system, due to the combination of different metals – copper, steel, aluminium, zinc and possibly lead – which react with each other in the presence of water to produce oxides and other residues. The fact that you have to regularly bleed gas out of the system might indicate a small leak on the return side of the pipework which is allowing air to enter, and this will increase the possibility of oxidation. On the other hand, the gas might be hydrogen sulfide (smells like rotten eggs, and ignites when a flame is applied), which would indicate a more serious corrosion problem.

Serious corrosion will result in a build-up of sludge over the years, which will eventually cause blockages. In your case, this seems unlikely, however, as your system has been drained down and refilled using a corrosion inhibitor. So any slight discolouration of the system water is unlikely to indicate a serious problem. Regardless of the water colour, the most important point is to check that there is always a sufficient concentration of inhibitor in the system water. Fernox and Sentinel both supply kits to test for this (available from plumbers' merchants). The method is to collect a little water from a radiator bleed valve, add tablets, and note the colour.

Or you could try the old trick of bleeding radiator water into a glass jar and adding a steel nail and a 1p coin. If the nail turns rusty after a month, then that will be happening to your radiators too, so you will need to add more inhibitor until the system stabilises.

you mentioned using an acid descaler.

I wonder if there is a possibility that traces might still be circulating in the water and causing corrosion. Eventually it will get neutralised by the remaining traces of limescale, and by reacting with the metal.

If the amount of sediment in the Magnaclean reduces each time, then it is probably just residual sludge washing away. You should find it now leaves just a black smear that you can wipe off with a tissue, rather than a layer that you could scrape off into a jar.

The X200 is supposed to make old limescale dissolve into the water, there will usually be Magnetite mixed into the hard deposits (making them black). I have not used it but I imagine the magnetite content released will circulate until it is either trapped by the Magnaclean, or settles as sediment.

There is a possibility that there is a tiny air leak on the suction side of the pump, drawing air in. Sometimes you will see white, black or green stain around such a joint. This less likely with your pressurised system.

doitall said:

Jeff Howell gives it to you straight.

... the gas might be hydrogen sulfide (smells like rotten eggs, and ignites when a flame is applied), which would indicate a more serious corrosion problem.

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It's not just corrosion which is the cause.

Fernox explains: Avoiding Bacterial Contamination

Gas in the system
Microbiological fermentation in a system could result in flammable gas. Methane gas, which burns with a blue flame, is most often found. Hydrogen sulphide (emitting a ‘bad egg’ smell) may also occur, and is associated with the presence of corrosive sulphate- reducing bacteria.

As to the source of the sulphur, it could be in the tap water used to fill the system! All depends on where you live! There is also a small amount of sulphur in the steel used to make the radiators.

I once saw a suggestion that only boiled water should be used for filling heating systems.

another possible source:

johnkirk said:

de-scaled using 13% sulphamite

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spelling unclear? sulphamite?

Several people seem a little confused on their chemistry!

Hydrogen is produced when the inside of the rads rust. It is odourless and WILL burn!

Very often there is also a very small amount of hydrogen sulphide which has a very strong smell indeed so only a small trace is needed.

I have never heard of this "Sulphamite" and wonder what it is.

When rads first rust the oxide is a reddish colour. Over a few weeks/months it oxidises further to the black magnetite.

With the correct inhibitor there should not be any/much further oxidation occurring.

The magnetite is inactive and does no harm apart from its blocking capabilities and if in suspension its pump bearing damage..

Tony

If you had a long run of pipe that had a slight rise in the middle, the air pocket in that pipe could remain while the circulating water moves under it. Over time, the hot water will absorb a bit of it or push a bit of it along. When the bubble comes to the boiler it diffuses into microbubbles which are generally deposited in the first radiator. They pass by an auto vent.

Or maybe not.

Hydrogen is in the water tony.

Hydrogen and oxygen are used to make fuel cells which in the very near future will be used to drive electric motors in our transport

JohnD said:

another possible source:

johnkirk said:

de-scaled using 13% sulphamite

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spelling unclear? sulphamite?

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I think he may mean Sulfamic Acid, which is frequently found in domestic products for removing rust and limescale.

He could well do, but he should say what he means!

His confusion is further evidenced by spelling it differently in different postings!

Thanks for some helpful responses above.

* Yes, sorry, I did mean to say Sulphamic (Sulfamic) Acid, and not sulphamite.

* The pump has been raised to the highest of the 3 speeds several times in order to dislodge possible trapped air, and the normal speed is set at the middle one. Surely any trapped air would have been pushed on by now (especially after 3 months) into a radiator? The pipework is correctly designed to avoid air traps.

* Given the system is pressurised to 2 bar surely any air leaks into the system would never occur, even immediately before the pump where the pressure difference is at its lowest but yet well above 1 bar?

* No rotten egg smells ever noticed when bleeding the system or removing the magnaclean top. (I think it is a FACT that hydrogen is odourless, although hydrogen sulphide smells of rotten eggs).

* There is no residual sulphamic acid remaining in the system. It was only ever introduced into the already drained heat exchanger (7 litres capacity), at the boiler itself, and although brimmed it never passed through any other part of the system. It was drained out and the boiler flushed several times via the heat exchanger drain off pipe. The whole system was then fully flushed at least twice after that before the X100 and X200 added.