Clearing central heating airlock

Discussion in 'Plumbers' Talk' started by CageUK, Oct 25, 2007.

  1. CageUK

    CageUK New Member

    I have just fitted a rad into a conservatory and both that and the rad I have fed from are no longer working and I'm suspecting that there may be an airlock.

    It is a two storey house and the rads upstairs are getting hot as are some of those downstairs. The rad that I had fed from had feeds coming from upstairs and this did not have a seperate draincock so I had to drain the messy way (by undoing the rad valves and have now put one in to the rad that I fitted that will service both rads. But because these rads are quite a bit lower than the flow and return pipes I think this is where the airlock is. I have tried draining water for about 15-20 mins to pull down some hot water but it only partially worked and only one pipe got warm (not hot).

    I have searched and found that you can blast cold water from your kitchen tap to clear airlocks in hot water systems, but can the same method be used for central heating systems with maybe putting a check valve in the attachment hose to stop contamination? The airlock I suspect is under the floor upstairs so it will be a major job if I have to get physical access to it!

    Any other suggestions very much welcome.

    Many thanks for your attention!
  2. before doing anything else you need to check you aint got the flow/return pipes crossed
  3. Little Snod

    Little Snod New Member

    have you bled them and did water come out?
  4. OllyUK

    OllyUK New Member

    Have you checked all the lockshields? Worked for me turn all lockshields off except the new radiators put heating on if they work then go round the other rads and turn the locksheilds on 1/4 turn.
  5. CageUK

    CageUK New Member

    Thanks for your replies!

    Yes bled both rads and got water coming out. I then used the drain cock and one of the bleed valves (not at the same time though) to try to get water movement.

    Re: the pipes, I matched the configuration to the existing rad ie the pipe that fed the main valve, is also connected to the TRV on the new rad and likewise with the pipe to the lockshield. It's a friend job so I can't re-check it at the moment but I'm hoping to get there tomorrow to try to resolve it.
  6. CageUK

    CageUK New Member

    Well the lockshields thing is certainly worth a go. It isn't just the rads that are cold though the entire length of pipe from ceiling to floor is cold. These are effectively the tailpipes to the rad and I have teed off of these for the new rad.
  7. Little Snod

    Little Snod New Member

    Before you mess with the lockshields, turn off all the wheelheads/TRVs to make sure that is the answer. Then rebalance the system
  8. heatyman

    heatyman Member

    Where you drained down the droppers,have you got air vents on the top of these legs? It's not uncommon to find you have a high point in either the flow or return. You can still 'bleed' the rad through the full leg. turn off the flow and return individually and try bleeding. If it won't bleed through one valve, you know where to start looking.
    Martin
  9. CageUK

    CageUK New Member

    Well, heatyman there nothing visible so if they are there they will be under the floor in the bedroom above with wardrobes and stuff on the floor. I could try bleeding the the rad through the individual pipes though.
  10. CageUK

    CageUK New Member

    Little snod, do you mean to turn off all the rads using the TRV's etc and just leave the two cold rads on to force the flow through them?
  11. Matt-52

    Matt-52 New Member

    I've had an air lock on systems before and used the hose pipe trick used which seemed to work well. I've also done it with a seperate pump forcing water round while you have someone else trying to bleed the rad(s). That also worked well. Maybe the flow and return are the wrong way round?
  12. plummit

    plummit New Member

    I would look at the system pretty much as heaty mentioned, if it worked prior to me being there, it will work again, You need to understand the system, and possibly mains back feed it. Check the f&e tank has an over flow pipe, also check that it is not primatic.
    The best rule is to not trust the customer, I have run my **** ragged, only to find a lockshield valve is closed, and they promised me that the radiator worked fine prior to me undertaking work on the system !
  13. CageUK

    CageUK New Member

    If I have been a complete dork and got the flow and return the wrong way around, would this prevent both rads from working? If so, I assume that just swapping the valves on the new rad will do the trick.
  14. Little Snod

    Little Snod New Member

    Little snod, do you mean to turn off all the rads
    using the TRV's etc and just leave the two cold rads
    on to force the flow through them?

    That's right. This will determine whether or not it IS and airlock OR whether the system needs rebalancing.

    Did you try it?
  15. plummit

    plummit New Member

    If I have been a complete dork and got the flow and return the wrong way around, would this prevent both rads from working? If so, I assume that just swapping the valves on the new rad will do the trick.
    Maybe, but probably not, read up on the trv's that you have and check that they are bi- directional prior to swapping over trv;' and lockshields.
  16. CageUK

    CageUK New Member

    Ok I got back to have a look on Saturday. Turning off all TRVs and putting the heating on successfully got hot water into Rad 1 (the existing rad) but not rad 2 (the new one). There was air in the system which I bled from rad 1.
    I had had a horrible thought that because I have teed off of the dropped 'tails' of rad 1 that this may be giving me the problem as the water has no incentive to go into the new rad. I then thought of plumbing the two rads in series but that would result in a loss of individual control of the rads.
    After a bit of balancing and particularly turning down of rad 1 I mangaged to get some hottish water into rad 2 but not at the level that I would have expected. The other rads are verging on scalding but the new rad is only hottish and a little cooler towards the bottom.
    Unfortunately my friend had to go out and I couldn't complete the tweaking so I shall pop back in the week.

    I have satisfied myself that the valves were in the right order (and the TRV is bi-directional).

    Any further opinions would be gratefully received. Many thanks for your help to date it has got me this far at least.

    Cheers

Share This Page