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New heat exchanger... Could it be kettling so soon?

Discussion in 'Plumbing and Central Heating' started by d000hg, 30 Apr 2019.

  1. d000hg

    d000hg

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    We had the exchanger replaced on our Baxi combi because we couldn't get hot water and kept overheating. Turned out to be all filled with sludge, since done all good.

    Until the last few days when I hear a frequent ominous rumbling lasting a few seconds each time, every few minutes.
    Looking online this could be kettling but could the exchanger have got messed up so quickly and if so, why would it not just cut out... We're still getting hot water just fine.

    How can I diagnose this better and is there anything I can do until the plumber can look (again!)?
     
    Last edited: 30 Apr 2019
  2. d000hg

    d000hg

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    Having a look at the boiler I do see when the rattling occurs the temperature shoots up to mid 70s, this is for demand for heating not hot water.

    More precisely the temp is sitting at 50 then it rumbles, THEN after that the temp jumps up.
     
  3. dilalio

    dilalio

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    If your hex was sludged up to the point of needing replacement, then it's likely that the rest of the CH system is also full of it and is causing circulation problems which is preventing heat getting away from the boiler. You'll need to get the rest of the system checked and cleaned. A magnetic filter should also be introduced on to the return, if you don't already have one. If you do, then check this for magnetite and clean as necessary.
     
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  4. dilalio

    dilalio

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    Which exchanger did you have replaced? I'm guessing it's the plate heat exchanger having re-read your op.
     
  5. d000hg

    d000hg

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    I think so if though I'm not 100% which that is. The very fine one used to heat hot water, only when a tap is turned on? That's what was replaced as one side was totally blocked with black sludge.

    Before that, we had had the CH system drained a couple of times. We have a magatec unit which had also totally sludged up and was cleaned out, then again a few weeks later.

    So are there two heat exchangers in use then?

    Based on my very limited understanding I'm struggling to picture how it can provide hot water without issues but not run the CH. I thought when you turned on a tap, it shut off the CH valves and recirculated internally over the exchanger.

    Anyway does what I described sound like it IS kettling? And is it urgent to get a plumber out?

    We
     
  6. Madrab

    Madrab

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    You will probably have a primary heat exchanger (HEX) that caters for the central heating and a plate heat exchanger that caters for the hot water but not sure as we don't have the boiler model. Given the fact that the plate HEX was all gunged up then the main HEX would probably be the same and the gunge may also be affecting the pump/system as @dilalio has mentioned.

    I'd say you should be looking to get the system flushed and cleaned and TBH should have been recommended by the person who swapped out the plate if it was that bad.

    Kettling is basically a low banging/rumbling/boiling sound as the water boils in the HEX and is either the flow through the HEX is restricted by either gunge in the HEX or the pump/system is restricted.
     
  7. d000hg

    d000hg

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    Sorry, the boiler is Baxi Duo-tec combi 40 HE A.

    My main worry is if kettling is dangerous firstly in terms of a steam explosion secondly in terms of a gas or water leak?
    Is it ok to use the boiler or should we be minimising use or even turning it off!? Waiting to get in touch with the plumber...
     
  8. ianmcd

    ianmcd

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    Not dangerous but needs to be dealt with, your boiler has safety devices that will shut it down before it becomes dangerous
     
  9. d000hg

    d000hg

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    Caught the plumber and he advises a full system flush using something that plugs in like a bigger version of the magnaclean.

    However his quote is £300 when he got back to me which seems a lot unless I've misunderstood and this is a permanent addition not temporary. He's been reasonably priced before and I'll ask him, but can anyone advise what they would expect this to entail and cost?
     
  10. dilalio

    dilalio

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    Find out if he's doing a Powerflush or a Magnaclense.

    £300 sounds cheap for a full powerflush but if a Magnaclense then it's a different method and treatment.

    You can youtube the two processes to get an idea of what's involved. I'd say it might be worth doing a mains flush with some cleaning chemicals left in for a few days, then draining and refilling with inhibitor.
    You can do this yourself for a few quid as time is the most expensive resource that you'd be paying a tradesman for. It might need a powerflush after all, but worth a try for the cost of a few bottles of chemicals.
     
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