Air in the system

Discussion in 'Plumbers' Talk' started by jalumala, Feb 11, 2018.

  1. jalumala

    jalumala New Member

    Hi, I'm trying to find the cause of the air in the system. Every time the heating starts there are three to four loud bangs in the pipes. Also I've noticed suction on the vent pipe as pump starts.

    Does this setup looks correct to you guys?

  2. The Teach

    The Teach Well-Known Member

    In the one supplied photo,The pipe configuration setup is ok ;)

    Why your system bangs,well that could a few reasons and onsite investigation is recommended,when was the system last serviced ?

    A cover on the wiring centre will be needed :(
  3. jalumala

    jalumala New Member

    The Teach, thanks for your reply.

    Serviced... hmm.. we have just bought the house so god knows when, but inhibitor was put in last in 2014 according to the label on boiler.
    I will probably get somebody to have a look and powerflush it, but first I want to put new rads (3 out of 7 done yesterday :) ) as the old ones are too small (boiler is rated 10-17kW and the rads were 7 maybe 8kW max alltogether).

    Can lack of inhibitor in the system (about a month now, as we were draining the system a few times) cause this banging?

    The cover is back already. I was in the middle of putting Nest when I took the photo.
    Last edited: Feb 11, 2018
  4. You've noticed suction on the vent pipe, Jal? That's a big clue.

    I think some of the causes in such a case include:

    F&E tank not high enough relative to the highest rad. Where's the tank, and what's the highest rad?

    Pump on too high a speed. Yours is on 2? - does the system work ok on '1'? If speed 1 sorts the sucking issue but the speed is now not enough to serve your rads, then possibly an new 'auto' pump could be the answer; this will fire up slowly (so no great 'suck' to empty the vent pipe) and will then modulate to serve the system's demands.

    A partial blockage somewhere - I'm guessing it would have to be on a return pipe so that the circulator now 'sucks' excessively before it as it ain't getting the return it wants, and this could possibly draw done from the vent? (That's guesswork...)

    Your pump is pumping downwards, I think - it's going to the 3-porter below. That pipe at the pump's top inlet that carries on upwards, where does that go?
  5. jalumala

    jalumala New Member

    Thanks Devil's Advocate, I think I tried it on speed 1, but it didn't resolve banging when it starts.

    The header tank is at the loft, boiler at ground floor and the pump upstairs.

    The said pipe goes to header tank, and the one next to it it's the vent pipe I believe.

    Would you recommend something like Sentinel x800 for a start? Leave it for a few hours and then fill and drain couple times?

    The central system hasn't been used for about two years before we moved in.
  6. The vent and F&E tank pipes that you mention are running parallel to eachother - are they 'linked' there just above the pipe, or is that teeing off somewhere else?

    If so, that pump will almost certainly be having a pretty major effect on the F&E tank - when the pump fires up, it'll be immediately drawing down on these supply pipes. I don't think that's ideal, but I'm not a plumber.

    You have tried it on speed 1, but the banging remains? Could that be because the system has already drawn air in at the higher speed so is responding to that?

    Can you make the banging stop at all? Does it eventually go away? If not, it seems that your system isn't very good at expelling any air it's drawn in.

    I really don't know what to suggest. There is no harm is adding X800 or MC5 or similar, but I WOULDN'T do this unless you first fit a Magnaclean filter to capture any released sludge; you don't want that stuff going in to your boiler...

    Also, the filter is the perfect way of analysing if sludge was the issue.

    IF you can make the banging go away - say after it's been running for an hour or so - then something to try would be to set the pump at 1 the next time it's used, and then slot it up to 2 after a few minutes; ie give it a 'soft start'. If this works - ie no banging this time - then a new 'auto' pump might be all you need.

    Or, a slight rejig of your plumbing. I'm not sure about the vent and F&E feed - I'd rather them not so directly 'in line' with the pump's action (but I'm only guessing here - you'd need a pro to advise properly).
  7. The Teach

    The Teach Well-Known Member

    the photo shows an old fashioned well known technique known as a close coupled H configuration,it works ok but has limitations.

    the pump pulls on the cold feed and any system air bubbles up the openvent,its a tried and tested configuration and works well until the system is extended or more powerful pump is fitted.

    there will be some vent suction on inital pump start but its evened out due to water weight in the vent & feed pipes.

    The H system has limitations,only onsite investigation will ensure its correct o_O

    Looking at the photo indicates its age so can only assume the boiler is similar vintage,renewal should be considered ;)
  8. jalumala

    jalumala New Member

    The both pipes goes parallel straight to the loft, 15mm pipe above the pump is the water feed and the 22mm is the vent pipe.

    I've just dipped the vent pipe in the glass full of water and then turned the pump on on ( on speed 1). There was slight suction, but it only took about 20-30ml from the glass so I think there is no way it can suck the air form here.

    Banging still occurs even on speed 1. But like I said before it only happens when the pump starts (knock, knock and that's it. It doesn't happen until next time we turn the heating on)
  9. jalumala

    jalumala New Member

    the boiler is Potteron Gold H 15. Don't have a clue how old it is, but it looks quite good and seems to be working fine (good heat, works really quiet and bills are much lower than in our previous house :D )

    EDIT. I've found the manual for it and it has "© 2014" markings, so it looks like it was replaced quite recently. Pump and 3 way valve looks quite new too (all that dirt is from sanding walls :D)
    Last edited: Feb 12, 2018
  10. The Teach

    The Teach Well-Known Member

    So a newish high efficiency low water content boiler on an old fashioned system,get the boiler serviced and ask for an additional job to investigate the system for banging noise o_O
  11. jalumala

    jalumala New Member

    Any good tips to carry DIY investigation? What else can be checked? What cancbe done before I will hire somebody. (I like to learn new things, and you know, when you buy a house.. every penny counts)
  12. IF you could eradicate that initial 'banging' - eg by never firing up the boiler on a pump setting greater than '1' - then chances are you've cured the problem which, I presume, is a stubborn glug of air still in there.

    So, IF you can do this, then the simplest DIY solution (hopeful solution) I can think of to keep it 'air-free' is to replace the pump with a new 'auto' type. Eg The Grundfos Alpha, although some swear by DAB pumps. In any event, you want one with an auto, self-regulating setting. Check with their respective manufacturers, but I understand they all start up 'softly' and then increase - and adjust - to suit demand , eg as TRVs open and close. I did fit a Grundfos myself for someone recently, and it's whisper-quiet, and fires up almost without you noticing - this one has an LED display, so you can see it's consumption - it creeps up and usually settles at around 18W.

    If there is trapped air, then a possible treatment is to fire up yer system (pump on '1') turn it up to 2 after 30 seconds, and then blast it at 3 - leave it like that for 5 minutes and hopefully it'll have driven out any glugs of air, whilst not drawing any extra in.

    If that works, then consider a pump replacement to prevent recurrence. Also, if it's easy, see if you can raise the F&E tank height.

    Any other solutions would involve rejigging the pipework, so it all depends if you are up for this?

    Also, seriously consider fitting a Magncleanse Pro and add a dose of cleaner - see what this collects. If the magnets are well coated, keep the dosing going until it remains clean.

    Then flush through and add inhibitor.

    (Another negative issue with drawing in regular glugs of air is increased corrosion inside the rads...)

    Treat all the above advice with 'cation' - ie only follow it if you think it's reasonable and might work. I am not a pro...
    jalumala likes this.

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