Ariston MicroCombi 23 MFFi Issue Heating and DHW

Discussion in 'Plumbing and Central Heating' started by Shinzo, 7 Dec 2019.

  1. Shinzo


    7 Dec 2019
    Thanks Received:
    United Kingdom
    Hi all,
    I have an issue with my Ariston MicroCombi 23 MFFi boiler.

    We lost hot water a few days ago, some diagnostics showed that the DHW temperature sensor / thermister was looking bad (low ohm reading), since this issue occurred every time we use the hot water the central heating wont fire up.

    Thermister on the DHW side has been replaced and we have hot water again but the other problem still exists.

    Goes like this:
    • Start / reset boiler
    • Heating (burner plate) comes on and goes off all good.
    • Hot water comes on and off no problem.
    • Whenever hot water is used and turned off the burner goes off - even if heating is on - pressure stays consistent.
    • If heating is on when hot water is turned on boiler pressure drops by approx 0.25-0.5 bar and the burner plate visibly reduces flame slightly.
    • Once the hot water goes off the burner also goes off so the heating goes off.
    • Turning heating on and off via the thermostat does not reignite the burner, although pump comes on and pressure increases.
    • After 5-6 mins the boiler resets itself and the heating will work again.
    • Failing this its a manual restart of the boiler.
    • Use the hot water and we are back to no heating and waiting 5-6 mins or a boiler reset.
    • Hot water will continue to work though.

    Any ideas?
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