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Reverse Flow to clear sludge

Discussion in 'Plumbing and Central Heating' started by joerice50, 9 Feb 2014.

  1. joerice50


    9 Feb 2014
    Thanks Received:
    United Kingdom
    Hi All.

    I ran into a short cycling problem with my Worcester Bosch CD30i which I believe is due to sludge. I found lots in the header tank despite having inhibitor I cleared most of it out but some has got into the system judging by the plugs of black gunge I get out of radiator drains when I fit a 1/2 bsp drain cock and vent through transparent pipe work.

    I eventually got the system hot and then drained the complete system fitted a magnaclean filter and dosed the system with two bottles of sentinal x800. I got lots of magnetite out of the magnaclan filter but boiler still short cycles, which I think is due to restricted flow either in the boilers heat exchanger or in the systems control valves. My rationale is based on the fact that the Grundfoss pump is rotating well and is impossible to stop with a screwdriver through the front vent plug and that magnetite is likely to build up at reduced bore restrictions in the system.

    Currently the boiler will short cycle and heat the system....eventually. Today I had a brainwave what if I flipped the pump over so that it sends water around the system in the reverse direction will this change of direction flush out the restrictions? So I did this flipped the pump and turned the boiler temperature low and ran the system ...It Works. But the boiler is still short cycling but I will try this reverse flow for a couple of days to see if it can dislodge the sludge.

    I have a powerfush booked for March so the above are just interim measures to try and improve the systems state prior to the power flush.

    Is there anything else I should be doing?


    Joe Rice
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  3. Gasop


    25 Oct 2009
    Thanks Received:
    United Kingdom
    Probably the pump is gunged up preventing a good circulation.

    Isolate the pump, remove the head and clean up the impeller
    making sure to get all deposits out of the channels and centre.

    Also whilst the pump is off hold a container under the outlets
    and open the valves for a very short time to check that the
    valves not partly blocked.
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