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Rust around gas boiler flue joints

Discussion in 'Plumbing and Central Heating' started by Marnhullman, 19 Jul 2021.

  1. Marnhullman

    Marnhullman

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    I have a seven year old Glo-worm 18hxi gas boiler in a second floor flat; the flue exits sideways onto a south west facing wall.

    A recent Gas Safety check reported that 'Flue has been leaking above boiler'; 'needs new flue'

    I have only just now discovered that other flat owners had reported water ingress into their gas boiler flues some years ago and they believe remedial action was taken but they don't know what was done!

    The installer of the boiler investigated and said he thought it was water ingress due to the exposed position of the flue outlet but was unhelpful so I contacted Glow-worm Technical department and asked whether they could supply a cover or baffle to stop any rain water ingress but they reported:

    "Our flues are stress tested so this fault should not occur and are designed so that any rain water which was to enter the flue should go through the boiler and exit via the condense."

    I replied:

    "Since, as you say, water ingress should not occur can you suggest why there is rust around the flue joints? Is this a problem you have experienced elsewhere and if so what is the cause and solution? I'm concerned that if I just have the flue replaced on a like for like basis the problem will recur.

    Glow-worm's response is:

    "If the flue was installed correctly and flue seals are in good condition and the boiler is burning okay then there is no reason why this would happen. Any flue extensions should be fitted with a fall back to the boiler. The flue should also be adequately supported at every metre or change of direction and if you have any external flue joints these need to weatherproofed using a suitable silicon sealant."

    I have discovered in the last week that the letting agent I use for the flat has failed to have the boiler serviced despite charging for a Gas Safety Check and Service. Only the Gas Safety Check has been carried out; the meter readings of the boiler were satisfactory, I believe, and the only fault found was the leaking flue so although the service should have been carried out and I will be sorting that out shortly I would have thought the Gas Safety Check would have identified any problem that could have caused the flue to leak?

    I would be grateful for advice and suggestions as to the possible cause of the leak and a solution as I'm not keen to just have a like for like replacement if there is an underlying problem that needs to be fixed.

    Thank you
     

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  3. kidgreen61

    kidgreen61

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    Flue needs to be dismantled, stains suggest the seals are leaking.

    Gas cert doesn't include a service, rather like your car MOT
     
  4. Marnhullman

    Marnhullman

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    OK but why would the seals leak? How do I ensure they won't just leak again?
     
  5. CBW

    CBW

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    Flue seems too steep toward the boiler, and agree with @kidgreen61, appears flue seals have perished and leaking.
    flue seals can leak over a period of time for a couple of reasons. I’d have the flue installation looked at.
     
  6. Marnhullman

    Marnhullman

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    What are the couple of reasons?
     
  7. CBW

    CBW

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    If the seal was damaged in installation, or if the condensate has rotted the seals.
     
  8. Marnhullman

    Marnhullman

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    OK. So how common is it for condensate to rot the seals i.e. how long should they last? Why do some rot and not others? Is there something that needs to be done to stop them rotting? Does condensate differ in its concentration and why would that happen?

    Looking for more solutions here.
     
  9. Madrab

    Madrab

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    Certainly needs dismantled and seals checked/replaced and the flue/seals 'sealed' properly so no water gets to the join ..... why the flue is rusting is a question for glowworm and what their flue materials they use.

    Agree too that the flue looks too steep a fall back to the boiler. It actually looks steep enough to pull the left edge of the turret up allowing the dripping water to run inside the case, that could mean the the turret to the room sealed case seal is compromised too, that needs checked urgently.

    Flue hole has been cut a smidging too high or more likely the boiler's been fitted a smidging too low to leave an angle like that :unsure:
     
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  11. MeldrewsMate

    MeldrewsMate

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    It looks like there is at least one flue extension (the original flue plus a cut-down 1m extension).

    I don't agree with the 'too steep' comments (the case top does not appear distorted), but would rather suspect a poorly cut extension with burrs has damaged the inner seal on assembly, the corrosive condensate having rotted the outer flue over time. The outer flue should only contain air from outside; a little rainwater too, but not enough to rot and stain like that shown.

    I agree wholeheartedly that an urgent inspection is called for, and any faults corrected. Fitted correctly, the new parts will last for many years, probably longer than the boiler.
     
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  12. Marnhullman

    Marnhullman

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    Thank you for the latest comments which offer reasonable explanations as to what may be the cause and therefore what to look for.

    I will get a heating engineer ASAP to investigate further and fix the problem.

    Regards to all.
     
  13. Lower

    Lower

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    I had exactly this fault with remarkably similar rust staining on a gloworm 24hxi.

    when dismantled, it was evident that there had been no attempt to deburr the cut telescopic inner flue which had damaged the seal.
     
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  14. Marnhullman

    Marnhullman

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    Thank you.
     
  15. Madrab

    Madrab

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    Not sure how else the water is getting from the outside of the case under the turret and down onto the internal combustion chamber if the turret isn't pulled up even a little by the angle of the flue? If you zoom in on pic1 you can see the body of the closest screw in between so there is definitely a gap, the back screw doesn't look tightened fully either.

    That being said it could also be that the turret isn't tightened to the top of the case properly.

    Either way to room sealed case is compromised.
     
  16. Lower

    Lower

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    Leaking inner flue seal at the telescopic joint. Condensate then drips onto the steel outer flue and runs back to the boiler, leaking at every joint.

    I had exactly the same corrosion and water staining on the same boiler.
     
  17. Marnhullman

    Marnhullman

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    Will it be necessary to replace the whole flue? I ask because it will be a challenging job to do that as it's a second floor flat and it would require scaffolding if the whole flue has to be replaced. If it's just an inner section that would be much easier.
     
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