Boiler with water at the bottom

Discussion in 'Plumbers' Talk' started by catrin morris, Oct 18, 2022.

  1. catrin morris

    catrin morris New Member


    I'm at my wits end trying to work out what's happening with my boiler and would love if anyone can give me some advice!

    We had a Mistral oil boiler installed a couple of years back when we had some renovations done on the house. The boiler wasn't kicking in some mornings and called out an engineer to come and have a look at when he opened the boiler there was about an inch of water sitting at the bottom.

    He was convinced that it wasn't rainwater, he even had another British Gas engineer come to flush our system who agreed.

    We contacted Mistral who came down a couple of times to look at it, decided the boiler was working fine - no pressure loss and exaggerated condense liquid by squirting water down tubes etc and said that it must be rainwater getting in due to a shoddy install (some rubber bungs were missing and not sealed properly).

    they sent me some seal tape to put around the doors and some more blanking plugs and to loosen the screw cap to the door panel as it was 'slightly out of true'.

    So, after much deliberation they agreed to come and replace the case of the boiler as there was quite severe corrosion and sealed it up, ensured that it was right and off they went happy that they'd gone above and beyond to help. They also suggested that we add a cover to the back between the house and boiler as rainwater could be falling from neighbour's roof onto boiler and causing driving rain to enter boiler.

    We thought that it was all good until it came to needing a service, and lo and behold, the engineer comes and there's water in the bottom and corrosion is pretty bad on the heat exchanger and suggests I take it up with mistral as he feels with water in the boiler it will fail in a year or so.

    Spoke with Mistral and they said that they have no idea where the water is coming from, they've done everything they can and will do no more. They said that the corrosion is only surface rust and wont affect the boiler, but if there's water in there then it's obviously going to interfere with the electrics.

    I find that it does fill up when it's raining (there isn't water in there when it's sunny,but the boiler is east facing and the water dries pretty quick with that morning sun, so it's difficult to say. I do feel that it is not up to me to work out how rainwater is getting in to a boiler which is supposed to be sitting outside in the rain?

    So - any advice would be greatly appreciated.

    Thanks in advance.

  2. quasar9

    quasar9 Screwfix Select

    I think you have answered your own question as to the source of the water, “ I find it does fill up when it’s raining” .
    Get the installers back and ask them to trace the leak which likely to be rain.

    in the meanwhile post as many pics of the installation, boiler and area of the flue etc so someone with experience in oil boilers can respond.
  3. heatyman

    heatyman Well-Known Member

    Is this an external boiler? If it is on a sealed system and there is no pressure loss, then it must be rain water.
  4. catrin morris

    catrin morris New Member

    Thank you for replying. I put the hospice over it just now and from what I can see the water is getting in through the front panel, from top and bottom!!
    31E842B8-A931-47AA-A678-C0010A370814.jpeg E4DA6564-73C3-414C-BA46-D3C81BCF3753.jpeg 700B6DA6-7EBD-413B-9C20-0ADE4881992C.jpeg 31E842B8-A931-47AA-A678-C0010A370814.jpeg E4DA6564-73C3-414C-BA46-D3C81BCF3753.jpeg 3F7DB489-9AB3-42A5-B341-72EB5DA6B75D.jpeg F6045DD5-75AB-493D-8603-135453A28D97.jpeg 64B079EC-DAE9-4814-8F01-D6A05E7D0605.jpeg EB4478B0-3F6E-4870-AF78-39604A0539CE.jpeg
  5. heatyman

    heatyman Well-Known Member

    Just a thought, as it is a combi, the only other possibility is a leak from the DHW supply side. I have serviced many of these and have always found the cases to be pretty water resistant. The fact that the side seals overlap the top seal means the top seal is not as water resistant as it should be, but even then only horizontal rain should penetrate it.
    catrin morris likes this.
  6. catrin morris

    catrin morris New Member

    I meant I put a hosepipe on the top. It was completely dry beforehand. When I was looking at the boiler during the day I could see light coming in through the bottom of the door.

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