Ariston 27 mffi DHW

Discussion in 'Plumbing and Central Heating' started by billm, 14 Dec 2017.

  1. billm

    billm

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    Hi, I have an Ariston 27 MFFI combi boiler, with only DHW running when I turn the Hot tap full on and the DHW Temp dial set at Max the temperature LED's on the boiler go up to 60 and no further.

    Is that correct as I have seen a YouTube video where the same model boiler lit up the higher LED's when testing the DHW.

    I'm wondering if the DHW temp probe on mine might be faulty ?

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  3. DP

    DP

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    Could be lack of proper service, inadequate gas pressure or excessive water flow during hot water demand.
     
  4. billm

    billm

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    Hi, thanks, I just tried it again with the minimal DHW flow and it still stayed at 60.

    But then I noticed something strange. The CH Flow pipe leaving the boiler was just as hot as the DHW pipe and stayed as hot until I switched the DHW tap off. And the CH hasn't been on for hours. When the DHW stopped the CH Flow pipe cooled off quickly.

    The reason I am checking the boiler today is while the CH was on at t-time, the DHW was'n hot, just warm, I was easily able to hold my hand under the tap. When the CH was switched off the DHW got hot but the LED's stuck at 60. Hence my original question.

    But now I'm wondering if the Diverter valve is not fully sealing and allowing hot water to flow out through the CH Flow pipe when DHW is requested.

    If so I think you can get a Diverter Valve repair kit that might be worth a try ?

    [​IMG]
     
  5. billm

    billm

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    I've bought a new Diverter valve instead of the kit and to avoid draining the complete house CH system I can shut off the Flow (A), Return (E) and Cold (D) with the valves under the the boiler and drain the DHW by running the hot tap (B)

    But I can't see any tap to drain the water that will still be inside the boiler heating circuit.

    Is it a case of uncoupling the Flow nut above its isolator valve (A) and catch the water there, at least it's outside the boiler enclosure so won't get all the wires & internals wet ?

    thanks
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  6. Yes; but you may also find that once you've done this, the heat still doesn't reach maximum, as you've also got a clogged up heat exchanger as well.
     
  7. billm

    billm

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    Yeah, I think you're right. I've replaced the Diverter valve and that has stopped the Flow getting hot when drawing DHW.

    The LED's are still at 60 max on DHW but I'll see how hot the shower is when the CH is on and if it isn't hot enough I'll replace the heat exchanger next.

    Is it worth putting an Inhibitor or something in the CH system when I've finished playing with it.
     
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  9. You shouldn't need to replace the heat exchanger, as it's just a case of descaling it. And definite on adding the inhibitor, just to be on the safe side.
     
  10. billm

    billm

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    Yeah I was thinking that is all it should need. How would you advise to descale the exchanger ?

    I was thinking I could remove it and soak in Spirits of Salt (a strong Hydrochloric Acid) for an hour or so with gloves and lots of ventilation for PPE purposes.

    Or can you do it economically while still in the boiler ?
     
  11. It needs removing unfortunately, otherwise you'd get the cleaning stuff in the system. The spirits of salts should do the job, but anything that descales will also work, just quicker or slower depending on the strength of it. Yes, be damned careful though. Add the salts to the water, not the other way round.
     
  12. billm

    billm

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    I've got hot water now so no rush for descaling it this close to Xmas. I'll get some Salts and give it a good soak in January.

    thanks for your advice & have a good one !
     
  13. Some accurate measurements of the hot water flow rate and the temperature in 0c will help diagnoise faults.

    Thats how the any decent repair technician will approach your fault,if it is actually a fault (breakdown) it could be set up incorrectly :idea:
     
  14. billm

    billm

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    Yes it probably needs that as well but as I had it installed 10+ years ago and we're in a hard water area, it only takes an hour or so to remove and descale the heat exchanger, I'll give that a go after Xmas and then do the measurements and balance the flow rate.

    cheers guys
     
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