Air in sealed heating system

Discussion in 'Plumbers' Talk' started by Chilla, May 5, 2016.

  1. Chilla

    Chilla New Member

    Hi, I have a bit of a puzzler (at least for me).

    I have fitted new radiators (some double panel and others cast iron ones) and rerouted some piping that went up the middle of the wall. But now one radiator keeps getting air in it. I know why it is just this radiator (there is a rise up from the floor below and then some poorly angled piping, so this radiator comes off a high point - like a bubble trap). But I don't know why the air is there.

    The system is sealed and hold pressure at 1.8 bar (I was away for 2-3 weeks and it did not drop a bit). I have inhibitor in, and the gas does not burn. But this morning I had to bleed almost the whole radiators worth of air (built up over a few weeks). Any ideas? I am very confused as the air only comes in when running, and I don't have to refill the system by adding new water.
  2. Blimey.

    (1.8bar cold is too high - unnecessarily high - so the next time it drops due to you bleeding, I'd leave it at around 1 bar to 1.2)

    You have trapped air?


    Ok, how can that 'air' get in there? These are the only ways I can think of:

    1) It is air that has yet to be purged from when you fitted these extra rads.
    2) Is it air that's leaking past the EV diaphragm.
    3) It is not air but gas produced as a by-product of internal corrosion.
    4) It is being 'drawn in' to your sealed & pressurised system from outside.
    5) Something I haven't thought orf.

    And the system pressure stays steady during all this? Blimey.

    So, (1) is possible, but you reckon you've bled it all by now? What you haven't told us is whether that rad has 'refilled' with air since you last bled it? Ok, I doubt whether you really did bleed off a 'rad full' as that is one HELL of a lot of air. Air might hiss oot the valve for a long while, but that doesn't mean it's actually a 'lot' of air.

    (2) is quite possible - this can happen when the diaphragm punctures. Obviously it'll stop doing this after a while, and you can expect some serious pressure fluctuations as it progresses - ie; when you bleed your air, the pressure should drop significantly, and then the pressure will likely soar when you turn on your CH system. But you say neither happens?! Blimey.

    (3) Possible, but surely not in the quantities you describe? And you say it doesn't burn?

    (4) Nah. Just can't happen. Nada. Nope. Yours is pressurised system, so no way is air gonna go in to your system. On vented systems, yup it can happen under certain circumstances. Unvented and pressurised, nope.

    (5) Something I can't think orf.

    Can you confirm - you have bled this rad a few times now? And the pressure remains constant?! And it keeps on filling with air?!!

    Does your pressure gauge move at all (what type is it - manual or digital?)?

    What boiler do you have?

    I'm stumped... All I can imagine is that the amount of air coming out each time is not as great as you think it is, and you are still expelling air from fitting the new rads.

    Something you could try is to bleed that rad again, and then shut it off fully at both ends. See if air now turns up in other rads, or have you 'sorted' the problem.
  3. KIAB

    KIAB Super Member

    Could be signs of electrolytic,or galvanic corrosion in the heating system, you have steel & cast iron radiators,plus copper,& maybe aluminium, you should have dose system with Setinel X800 cleaner & left it in for few weeks,then throughly flush system, before fitting new radiators & adding inhibitor.

    Also if a combi, then it should have a program to purge air from the system.
    Last edited: May 5, 2016
  4. heatyman

    heatyman Well-Known Member

    When you next bleed it, turn off the flow valve and bleed it, then turn off the return, open the flow and bleed it again. Bleed off about 1 litre a time. Bleeding with both valves open can enable one side of the system to stop another bleeding.
  5. KIAB

    KIAB Super Member

    And bleed it with boiler switched off.
    philthespark likes this.
  6. Chilla

    Chilla New Member

    thanks for the replies.

    I think the system is fully bled now. I have bled this radiator quite a few times now (over several months). I refilled/bled the system with the boiler off, but didn't know radiator bleeds needed it off (it never drops the pressure much).

    Having thought more about saying the 'whole radiator needed bleeding', I don't think this is quite right. I though this as only the bottom inch was warm, but that is because it is not circulating (duh), having said that it must have been about 1/3rd of a 600x600 Double rad with how long it too to bleed.

    Pressure vessel: I think more air than could be contained in the vessel has been vented, and the pressure seems well behaved. (ps The 1.8 bar is because the house is very tall and thing (4 stories), do you think it is ok to drop to 1.2 bar?). And it is a needle guage (old CDii boiler).

    Electrolytic,or galvanic corrosion: Don't know anything about this, but I definitely did not use X800. I did put in 2 litres of x100 though. Could this be an issue still? (also I bought some x300 that was onsale a £2 a litre a closing down B&Q). I had discounted rusting due to lots of inhibitor, but also the cast iron rads don't evern need bleeding (just this one that is badly placed). So I thought they cannot be rusting.

    Finally, I was wondering if the pump could be drawing in the air, as I am sure it gets worse when the system is used more.
  7. CraigMcK

    CraigMcK Screwfix Select

    does the pressure gauge ever change. IE is it stuck? If you vent off say 1/2 rad of air, it's now filled with water that would automatically drop the system pressure, it must have filled the rad with about 2~3L
  8. So this situation is continuing, Chilla? How often do you bleed air from that rad? And the system pressure doesn't drop? Blimey...

    If the 1.8bar pressure doesn't go any higher when the system is hot, then there isn't really an issue with that level. But it still strikes me as being high.

    The height of the system shouldn't - I don't think - have a bearing on this - it's a different kind of system pressure (ie now't to do with gravity).

    But perhaps plumbers can advise on whether a 4-storey system should be pressurised higher?

    I still don't understand how your pressure doesn't drop when you bleed, tho' (sounding gory). I know it's a largish system with a fair capacity, but still...

    Are you sure the system pressure doesn't fluctuate in use (between hot and cold)? Are you sure the gauge is working?!
  9. CraigMcK

    CraigMcK Screwfix Select

    Hey DA, stop trying to steal my thunder, the pressure gauge working is mine, you had your chance at asking that question :)
  10. Yeah, but it's the last person to mention it wot gets the credit. :p

    Chilla - can you check the gauge...?
  11. Chilla

    Chilla New Member

    Ha :) So the pressure goes up (from memory) about 0.1-0.2 when hot. It also drops to zero when the system is drained and builds up sensibly when refilling the rads. I am obv not a pro, but it seems to work fine to me...

    After venting the rad it might have dropped and I did not notice it (as it was warm), but I think def not more than 0.05-0.1 bar.
  12. So the gauge probably works...

    What's the situation now, Chilla? Are you still gettin' air?

    And when you bleed it out, the pressure only drops a tenth of a bar max?!


    Do you have a second EV on your system due to the number of floors/rads?
  13. Some people like posh words galvanic corrosion ill r ember that till I die have you by any chance just done a 6 week course lol
  14. KIAB

    KIAB Super Member

    No, over 30 years, it's all about noble metals, rather like humans, some you like, some you don't & others you tolerate.:)

    That why you find sacrificial anodes in the header tank in Elson cylinders & indirect cylinders,etc.
    It why you put a inhibitor in a seal heating system to avoid galvanic corrision.
    Last edited: May 5, 2016
    Deleted member 33931 likes this.
  15. KIAB

    KIAB Super Member

  16. well noted but firstly why would you like to know so much about sludge I don't need diagrams to show me how it occurs unfortunately sludge or galvanic corrosion will soon be a thing of the past and us who know about y plans and s plans and oh yes don't forget the w plans will be a thing of the past no more pumping over
  17. KIAB

    KIAB Super Member

    Some plumbing & ideas are so old fashion today, open fires with back boilers, or having header tanks in the loft in the 21st century.:(
  18. I know Christ if somebody asked me to install one I'd be gobsmacked . Proper heating engineering is dying out its become a combi / nation almost as if people nowadays view it as a joke . Let's face it anyone can fit a combi . Them boilers have tarnished what was once viewed as a skilled trade
    KIAB likes this.
  19. Chilla

    Chilla New Member

    So back at home and with cold radiators: the venting caused a 0.2 bar drop [my guess work is real bad]. Only 1 EV, but it is a big system (so)...

    I *think* [though I am double guessing myself now] that the system does not create air when the heating is off (but perhaps it needs to be circulated). Definitely the system did not loose pressure over a 3 week period that it was not used (I set the red needle gauge).

    But now I am really confused:
  20. KIAB

    KIAB Super Member

    The reason we are a combi nation is people's lifestyle have changed drastically, just look at the changes in plumbing for the last 30 years, it's frightening, & it's no different with other trades.

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