Bleeding radiators

[Gwenoakes]

It must be the day for daft questions from me, but..........I have just been round the house bleeding the rads and suddenly wondered how on earth air got into water pipes. Anyone know?

[p.penn]

Possibly because water is H²O - 2 parts hydrogen to one part oxygen, and perhaps the oxygen gets a bit shaken about by the central heating pumps and rises to the surface?

I should have been a scientist you know

[Gwenoakes]

Wow! I am impressed ppenn. LOL

You sure you have not been googling before you replied?

[AL37]

Hi Gwen,
Helen isn't that far off the mark. Its mainly down to electrolysis, water reacting on the pipe work producing a gas. A bit like a car battery on charge. Also as you heat water gases are released (as Helen said) . You can add stuff to the system help reduce this meaning you have to bleed the system less often.

[saint-spoon]

To be honest Al I hadn’t heard the electrolysis theory before and I have worked on some pretty big water filled heat exchangers before now; an interesting idea anyway and one which I shall investigate more thoroughly at a later time. Anyway the gases that make up the air around us will readily dissolve into water and when heated the gases are forced out to form bubbles which then group together and collect in areas such as the top of radiators. If you empty your heating system and refill it you will have a lot of dissolved gas that will collect and need bleeding off regularly after it has been expelled then the system should not need bleeding as often so long as it is devoid of leaks.

[saint-spoon]

by the way air inthe system can encourage corrosion

[Gwenoakes]

Well, I AM impressed, thanks very much. Not too keen on the 'corrosion' bit though, will have to watch out for that.

[Don Roberto]

Beware folks, if electrolysis is taking place the gas in the radiator may well be hydrogen, so don't smoke whilst bleeding radiators. If the water released is very black, electrolysis is the most likely scenario. A suitable inhibitor will go a long way to stopping electrolysis, and remember that the inside steel of your radiator becomes a sacrificial annode and can very easily become holed. Cheers me dears.......

[Gwenoakes]

Well, thanks for that DR, although I will be thinking about that now. The water is not black that comes out, but the only rad that always needs bleeding is corroded at the bottom, i.e. going slightly rusty. Do I need to be worried..........yet?

[Don Roberto]

If the rad that is rusting is in the bathroom near the loo then there is nothing to worry about. Steam and stray splashes from dads and sons are often the cause of such rusting. Light sanding and a good undercoat and top coat of paint will do the trick. The regular need for bleeding can be caused by simply that rad being the tallest rad in the property, or maybe the circulation pump is set on too high a speed I turned my pump from 3 down to 2 and although it takes the rads longer to heat up I rarely need to bleed them. Hope this helps Gwen. Cheerio me deario.......