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Discuss Vaillant ecoTEC plus 837 R1 with persisting F75 fault in the Central Heating Forum area at UKPlumbersForums.co.uk.

  1. yossibac

    yossibac New Member

    Can someone help diagnose Vaillant ecoTEC plus 837 with persisting F75 fault please?
    We already replaced the pressure sensor, installed F75 kit, replaced the main heat exchanger, and the pump, and the PCB, and flushed the system and installed a filter on the return, but still sometimes we get F75. The boiler still reset and run, but we would like to get to the bottom of it if at all possible. Thanks in advance.
     
  2. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    Who did the work ?
     
    • Agree Agree x 2
    • Like Like x 1
  3. Noxer

    Noxer Member

    Blocked flow sensor?
     
    • Disagree Disagree x 1
  4. Riley

    Riley Plumber GSR

    Wow that’s some repairs
     
    • Agree Agree x 1
    • Funny Funny x 1
  5. yossibac

    yossibac New Member

    All those parts has been replaced in the course of 5 years not all at ones, and from different reasons, but the F75 has been creeping out all this time, some times the fault would be gone for months so you think that it was cured. The boiler is otherwise working well. There are two questions: 1) if there is a fault why the boiler always reset and continue to work sometimes for months? 2) if there isn't a fault why is the F75 keep creeping out? Thanks for your thoughts.
     
  6. Nico

    Nico GSR

    Do you have to top up the pressure in the system often?
     
  7. yossibac

    yossibac New Member

    Yes, every three months or so, and it does seem to keep F75 away for a while, we are now on 1.8 bar when cold and 2.1 bar when hot
     
  8. Nico

    Nico GSR

    I believe F75 is a fault code for when boiler pressure is too low/ also doesn’t detect an increase in pressure when pump kicks on. Have you ever noticed what pressure your boiler is sitting at when this code is showing?
     
  9. yossibac

    yossibac New Member

    I noticed that if the F75 starts kicking and if after the first reset F75 returns, it makes it calm down if I top up. Last time boiler was at 1.7 bar before the first F75 kicked in. Generally speaking Vaillant have different fault code for low pressure and the boiler can work very well with 1.2 bar or even a bit lower, but that only if the boiler is not faulty.
     
  10. Nico

    Nico GSR

    ah Right could be a number of things. Sound like a defect in the sensor or it’s partially blocked if it needs such a high pressure to pick up anything. Has your expansion vessel ever been investigated as well as everything else you had mentioned?
     
    • Agree Agree x 1
  11. yossibac

    yossibac New Member

    I will check the vessel. After installing F75 kit is it best to leave the bottom sensor connected or it's best to disconnect it's plug?
     
  12. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    Best to get a gas safe engy
     
  13. yossibac

    yossibac New Member

    We are:)
     
  14. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    So you won't need know the question you asked
     
    • Agree Agree x 1
    • Disagree Disagree x 1
  15. yossibac

    yossibac New Member

    I thought that this forum is there to help one another, so sorry for troubling you.
     
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