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Cream-coloured foam in header tank

Discussion in 'Plumbing and Central Heating' started by SK10291, 13 Nov 2021.

  1. SK10291

    SK10291

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    I have a very old system with a back boiler, and a header tank in the loft. It has a TF1 filter, fitted 5 years ago, but has largely been neglected over the years.

    In September I tried the heating and it wouldn't come on. Also, the header tank was full of brown sludge, which I cleared out. Turned out to be a blocked cold feed so cut out some of the pipe to clean it all out and closed it up again. This worked, and then used a bottle of X400 cleaner. Left it 4 weeks, but didn't seem to work brilliantly well. Flushed and drained thoroughly before replacing with x100 inhibitor.

    For the last month, the heating has worked reasonably well - except it has air in it. For the first few days after refilling, I bled all the radiators several times but could hear air in the pipes and pump immediately after bleeding all bleed points.

    Today, I checked the header tank. The inside of the lid was covered in condensation, the water is already a bit murky and brown, and there was a pool of creamy foam in the corner, under the expansion pipe. The Grundfos pump is on the slowest setting. The pictures below show the tank (after I had removed the foam - should've taken one before - but you can see some residue in the bottom left corner) and a close-up of the foam.

    I had hoped that, with the inhibitor in, I could leave it for the winter, despite the air. But now with the foam too, what do you think I need to do and can it wait until next summer? It's already an old system and boiler which has been corroding for years.

    [​IMG]
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  3. oldbuffer

    oldbuffer

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    1. Did you bleed with the system on or off. If on, water flow can push air round even while bleeding. Best bet is run system, turn off, leave for 10 minutes, then bleed from upstairs to downstairs.
    2. Have you bled any air out of the hot water cylinder primary coil, the one the boiler water circulates through?
    3. Have you bled the pump?
     
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  4. SK10291

    SK10291

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    1) Yep - always bleeding with the system hot and off
    2) No. I have no idea how to do that on my back boiler
    3) Yes, always bleed the pump with the rest of the system

    Any ideas on the foamy stuff?
     
  5. Madrab

    Madrab

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    If there's condensation in the F&E tank and foam and given the pic with the brownish section under the vent I'd guess it's pumping over.

    Run the system and pump and see if any water is running from the vent. What boiler is it? Is the system fully pumped or given the back boiler is it just pumped CH with gravity primaries for the HW?

    You may still have a restriction in and around the feed and vent where it joins the main system. Get a magnet out and touch it against the pipe around the branches.
     
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  7. SK10291

    SK10291

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    Thanks. I'll try observing the vent pipe. It's a Baxi Bermuda. I don't know whether it's fully pumped - how do I tell?

    Using a strong magnet, there's no attraction on the feed anymore, but there's some weak attraction after it tees in and onwards. This pipe is 28mm, though.

    Ok, so you think it could be due to partial blockages? I forgot to mention that I often hear a big rush of water coming into my radiator. Does this, together with the noisy pipes, suggest the problem is air/airlock in the system? Would that even cause pumping over?
     
  8. SK10291

    SK10291

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    Also, would turning the back boiler setting down (from 3 to 2) help a bit?
     
  9. HERTS P&D

    HERTS P&D

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    Is the top bend of the vent pipe be 40 cm above the water level of the F&E tank? The top of the bend should be at least 40 cm (15.75 inches) higher than the surface of the water in the cistern. ... This problem is known as pumping over, and will enrich the water in the cistern with oxygen.

    Andy
     
  10. Madrab

    Madrab

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    If you are getting some attraction to the pipe then it is at least furred up which could be causing a restriction allowing the pump to push the water up the vent, ergo pumping over, especially if the restriction is after the vent. Either that or where the pump is positioned in relation the vent along with the restriction. Hard to say without seeing the system.

    Turning down the CH temp won't change anything. Yes, there could be airlocks, especially if you've emptied the system and if the HW is gravity.

    Older Open Vent systems like these are notoriously difficult to work with once they have been played with/altered/drained etc All you can do is persevere
     
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