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New boiler - suddenly radiators needing to be bled weekly

Discussion in 'Plumbing and Central Heating' started by highwaystar, 10 Jan 2015.

  1. highwaystar

    highwaystar

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    We never had a problem before the new boiler but now air keeps gathering and practically every week it is noticeable that the upstairs radiators become cold at the top, I then bleed the upstairs radiators - loads of air to let out - I do all that with all the upstairs rads till all of them have no more air (till very small amount of water spurts out) and then all of them are hot at the top of every rad. A week later and back to the start - air has gathered at the top inch or so of all the upstairs rads and I have to do the same again. We never had this problem with the previous boiler - a combi - but now we have this new boiler - a condensing combi - since it was recently installed we've had pressure problems and air gathering that needs to be let out. That's been the only change - the boiler. Anybody know what could be the problem? Any advice would be appreciated. Thanks.
     
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  3. Burnerman

    Burnerman

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    Fresh water does contain lots of dissolved air which does take some time to expel, and this of course does interfere with the pressure in our combi.
    Maybe just give it a while longer. Did the installer renew the inhibitor, do you know?
    John :)
     
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  4. highwaystar

    highwaystar

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    Many thanks for your help.

    In answer to your question. I think he did. However, there's been pressure fluctuation problems from Day 1 (initially it was actually losing pressure then suddenly picking up pressure). Wish we'd kept our old combi (of the same well known make), it was far easier to use and steady and reliable as anything. Since we got this new one, the pressure has been up and down like a bleedin yoyo - horrendous. The manufacturer ended up sending one of their engineers and he found that the expansion tank within the boiler was 2 or 2.5 times the spec pressure - apparently its a bought in item and then added in at the factory, seemingly only tested that it worked on the test-bench in the factory and not tested for its pressure and/or it wouldn;t have picked up the pressure problem over a period of time of a couple of weeks even as we found. The manufacturer's engineer explained that the expansion tank allows for fluctuations in pressure in the system - but by the expansion tank being so over pressure it wouldn't have allowed fluctuations to happen normally and the pressure would have kept soaring - as it did - it was away up to nearly 3 bar and not yet in the red but not far off. I phoned them and took advice to let some water out which I did (took a while) by bleeding a radiator. This took the pressure back down to about 1.5 bar. However, when the manufacturer's eng came he drained the whole thing and started again - he reduced/set the pressure in the expansion tank to the correct pressure as spec - and then he filled the water back up to 1.5 bar. That was about 4 weeks or so ago and since then I've had to keep letting air out.
     
  5. Burnerman

    Burnerman

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    Typically, the air pressure in the expansion vessel is around 10psi. This pressure can only be accurately set when the water pressure in the system is zero so it sounds like your second engineer is right.
    The water pressure in the system is then increased to the recommendation - 1.5 bar in your case.
    This pressure should remain constant but should rise to about 1.8 bar with the heating on.
    Bleeding air out of the system will reduce the operating pressure, so this is increased again by allowing water into the system by the filling loop so do become familiar with this.
    If too much water is introduced into the system the pressure will increase, and a pressure release valve will open at 3 bar and allow the water to escape to the outside.....the correct pressure can be obtained by bleeding water out of any radiator.
    Obviously the more fresh water introduced to the system means more air so this should be minimal.
    Finally, if your system is dirty, the gunge inside (magnetite) produces hydrogen which can be lit -believe it or not - at the radiator bleed valve.
    I hope this helps with the understanding of your system!
    John :)
     
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  6. highwaystar

    highwaystar

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    Hi John,

    Seems there is no magnetite left in the system - the manufacturer's engineer drained everything and started again and I think he only fed in fresh water.

    Our system isn't dirty - any water that I've let out and collected has been clear - and its a new boiler anyway, the whole system (rads/pipework) was power-flushed, new TRV's, new boiler fitted, magnetic filter fitted at the same time.

    I reckon its just the system being full of fresh water that, as you say, is often full of dissolved air and which will take time to settle down - maybe need to get the plumber to re-fill with magnetite treated water?

    I'm familiar with the pressure cold / pressure hot thing. Our old (Worcester) 280 combi was usually just above 1 bar (maybe 1.1 or 1.2) when cold and more like circa 1.5 bar when hot. The new 38CDi is supposed to be 1.5 bar when cold and when it is it rises to circa 1.8 bar when hot - of course when the pressure cold has fluctuated/increased to nearer 2 bar the pressure hot has gone to over 2 or nearly 2.5 bar - time to release the pressure by bleeding a radiator and the water has been almost clear enough to drink. The old 280 was a lot more steady in its pressure and easier/simpler to use imho, we replaced as it was nearly 20 years old and we were having a whole new kitchen anyway so it seemed daft not to renew the boiler as well at the same time - we've saved on maintenance plan costs (circa £230 per year) as we have an 8 year manufacturer's guarantee - net of the annual service of say £60 or £70, that's £150 x 8 years i.e. about £1,200 saved on maintenance costs, and that's not counting the savings on running costs as the new condensing combi's are more efficient so we should save on heating costs.

    Thanks again.
     
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  8. Burnerman

    Burnerman

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    My apologies if I have misled you here.....magnetite is the gunge inside a heating system....its in fact rust with an oxygen molecule missing.
    No matter - it sounds like your system is in very good order, and a quality inhibitor plus your filter should keep it that way!
    Be lucky
    John :)
     
  9. highwaystar

    highwaystar

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    Yep, that figures. :cool:

    Seems the inhibitor which plumber put in when the boiler was installed has been drained off when the manufacturer's eng came. So seems I need to get some inhibitor put back in - I assume it is just "added" like any additive and doesn't need to have the plain fresh water drained. I guess I should ask the plumber to come back to add this back in?
     
  10. Burnerman

    Burnerman

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    Personally I tend to go overboard with the inhibitor (but it has paid off so far).....I would definitely recommend it.
    I use Fernox F1 which is a gel type which is injected through the radiator bleed valve, but my rads have a bleed valve at one end and a blanking plug at the other so its easy to do with the rad closed off.
    John :)
     
  11. highwaystar

    highwaystar

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    I was thinking Fernox myself so will ask plumber to add in.

    The air in the system still seems to be increasing which I find puzzling - the area at the top of the rads that is cold is increasing which seems to indicate that the amount of air in the system is increasing (and so is the pressure rising at cold per the dial on the boiler) - yet not much more than a week ago I had bled all the rads upstairts and sealed them all tight again and there was no air at all. I can't figure why seeing as it is several weeks since there was fresh water topped up in the system, can't understand it :/
     
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