Bleeding radiators - spluttering

[gaj2002]

Hi, I have recently had some work done on our central heating system and am trying to get rid of the air introduced (which might be the subject of a longer post another time).

When I read on the internet (including this forum's FAQs) about bleeding radiators, they always say wait for the hissing sound to subside and then stop when the water is coming out.

However it doesn't seem to work like that for me, at least not always. Quite often I seem to get a mix of air and water. Also sometimes it seems like I get a flow of water, but if I open up the bleed valve another quarter turn then I get another hissy mix of air and water, then maybe that will subside, but if I open the bleed valve further then I get another hissy mix of air and water....

We have eighteen radiators in the house, of which four are towel radiators, of which two are very nice looking ones but they have the bleed valves on the underside of the top bar, I'm guessing that is a case of aesthetics over function. Those two are the worst for a hissy mix of air and water, but I also sometimes get it from the other radiators.

So I suppose my question is why does this happen and should I just be getting lots of towels and keep on bleeding until I can open the bleed valve fully and I'm satisfied I'm drawing only water out rather than a mix?

Thanks
Gavin

 

[denso13]

eep on bleeding until I can open the bleed valve fully and I'm satisfied I'm drawing only water out

Basically yes, keep going till no more air.

 

[Madrab]

So I suppose my question is why does this happen and should I just be getting lots of towels and keep on bleeding until I can open the bleed valve fully and I'm satisfied I'm drawing only water out rather than a mix?

The top of the rad is constructed in such a way that air and water can mix until it's all bled through.

Try bleeding it into a cup, it'll save all that towel washing and yes, as suggested, keep going until it's just water.

 

[gas112]

And bleed it with heating off

 

[Deleted member 267285]

Is it just first floor radiators? Do you have any pipework in the loft? Do you have any additional air vents?

 

[gaj2002]

Is it just first floor radiators? Do you have any pipework in the loft? Do you have any additional air vents?

We have a converted loft with two radiators (bedroom and bathroom). First floor has seven radiators, ground floor has nine radiators.

It has been the first floor and loft floor with the issues - certain radiators not coming on (the two in the loft and one on the first floor), possibly with the supply pipe feeling warm, possibly not. Easily fixed by turning off all ground floor radiators as that forces the supply through and dislodges any air, which can then be bled off, I suppose my issue is I keep on having to do this and I would have thought I would have found and expelled all air from the building works by now. 95% of water is clear, 5% is dirty.

The boiler (Ideal Logic Max S30) and hot water cylinder (UK Cylinders Prolite Air 300) are both at ground level in the garage. The previous system was a combi system in a different location.

I'm not aware of any additional air vents.

Any ideas?

Thanks

 

[gaj2002]

I should also add that one time I tested the "air" and it didn't ignite in any way so I think it is air rather than corrosion gases

 

[opps]

The top of the rad is constructed in such a way that air and water can mix until it's all bled through.

Try bleeding it into a cup, it'll save all that towel washing and yes, as suggested, keep going until it's just water.

Cut up plastic milk cartons are more flexible (and thinner walled)...

I additionally use them to mix powder based filler, epoxy wood hardener and as throw away paint kettles.

 

[Madrab]

Yeah, I use them as spirit holders for cleaning brushes. Not exactly recycling them though