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Discuss Vaillant boiler with a possible poltergeist! in the Gas Safe Register Forum - Public Forum area at

  1. Emkew

    Emkew New Member

    Vaillant EcoTec 931 R1 47-044-32
    I have worked in this industry for over 40 years and never experienced this. One of the issues being that the boiler is fitted in a property that I own and rent out. Apologies for the length of this post but it is a long and involved story and if any of you have experienced this or can suggest any explanation I would be grateful.
    The tenant contacted me on a few occasions stating the boiler was loosing pressure and failing to F75. This was happening at random times, sometimes a few days apart and sometimes a month apart.
    I inspected the boiler and system and there was no evidence of leaks.
    Tenant goes away for Christmas, Ahah! my opportunity to find out what is going on. I checked the fault history and the last 10 faults were F75. So the system obviously was loosing pressure.
    Thinking the PRV may be worn I switched the boiler off and attached a zip lock bag to the PRV pipe outlet outside. (tight enough to catch any spills but loose enough to be blown off if the PRV dumped completely). Checked after two days no pressure loss, no water in the bag. I removed the condensate pipe from the heat exchanger and left it open above a piece of paper to check if the heat exchanger was leaking internally, no joy. Pipe re attached.
    Next with the aid of a mirror and torch (access underneath is less than manufacturers specs) I discovered that the flow and return valves could be operated with an allen key as I had been struggling to try and close them with a stubby screwdriver.
    System isolated, pressure marked on the gauge. I will find out if the leak is on the system or the boiler. Returned two days later to check on progress. Water in the zip lock bag outside (goody), but when I went inside the pressure gauge was straining passed the red section. There was water dripping from the case. I removed the case, lowered the pressure and saw that the water was coming from the expansion vessel seam.
    From this I deduced that
    1. The PRV was not operating correctly as it should have kept bleeding the pressure off above 3bar (the gauge on the Vaillant doesn't have any figures as you will be aware)
    2. The expansion vessel needed replacing
    3. The plate heat exchanger must have failed to cause the increase in pressure.
    As I am writing this I realise that the integral filling loop could also have caused the increase in pressure, but lets leave that for now.
    I reduced the system pressure and dried the case out checking no water had gotten into the electrics. I turned the boiler on but it refused to fire showing F32. After several attempts the result was the same, so as the instructions were not much help I called Vaillant's technical help line where the lady I spoke to took me through the necessary electrical checks and readings to ascertain where the issue was. During these tests the damned boiler decided to start working with no obvious reason. The Vaillant tech suggested it might have been a loose connection, but I am not convinced.
    After a visit to the merchants and lightening my wallet by two hundred pounds, I returned to fit the parts. (PRV, expension vessel, plate heat exchanger).
    I isolated the cold supply and drained the boiler (still isolated from the system). I changed the parts and went to reestablish the cold supply by turning the valve back on, but there was no sound of water as expected. No water coming from the hot tap (the cold was working). I messed with this for ages but to no avail. I decided to remove the valve for inspection but that was going to be difficult due to the lack of clearance underneath the boiler. I turned the main stop tap off to remove the valve but then I stopped. (When changing a plate heat exchanger I always turn on the cold water first and check for leaks so that I know if a leak does occur which side it is on). I remembered that the system was still isolated. I turned on the system valves and the system pressure rose slightly as I would have expected. I turned back on the cold mains and water started flowing through the hot tap. I pressurised the system checked the boiler as I always do and waited for the system to get up to temperature. Once I was satisfied the heating and water were working I packed my tools and ran away.
    So far (three days) there has been no further issue but I am not completely convinced that this is the end of the saga.
    Any suggestions or insight into what I have experienced would be gratefully received.
  2. CBGAS

    CBGAS New Member

    I've changed loads of the cold water Inlet valves on Vaillant boilers (ecotec) as they pass water into the boiler when off and over pressureise it
  3. Emkew

    Emkew New Member

    Thanks for your input. I think I will get a replacement cold water valve to change at a future point as it is obviously giving some problems.
    However when the boiler over pressurised the cold valve was in the on position it was only the flow and return valves to the heating that were turned off. So I ruled this out as the reason.
    We are now five days in and so far (touch-wood) no pressure loss. Fingers crossed. But I would still be interested in everybody’s input as there are so many anomalies.
    Thanks again for your input.
  4. heatservice

    heatservice Member

    The ecoTec internal filling loop is very expensive and not fit for perpose as so often both valves let-by, if possible cap it off and fit an external one.
  5. Vee

    Vee Plumber GSR

    All I'd say is that working in this industry even after 40 years there is always another first, to forever keep an open mind, because otherwise its time to give in. Sounds perfectly ok.
    • Agree Agree x 1
  6. Emkew

    Emkew New Member

    Thanks Vee
    You are absolutely right. Sometimes experience can blinker you to new possibilities.
    The boiler has held its pressure for a month until last Wednesday.
    Due to family illness I haven't had a chance to fit the new cold fill valves that I have bought. I am tempted to monitor it for the next few weeks and see what happens.
    Thanks again for your input.
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