Central heating deposits

Discussion in 'Plumbers' Talk' started by Bodgitandlegit, Nov 30, 2011.

  1. Hi All

    The performance of my CH had diminished recently - with the upstairs rads staying cold - only the downstair rads warming up. Also the reheat time on the hot water cylinder was extended. I decided to use a chemical cleaner, followed with a drain and flush. I had a new pump and isolator valves ready, as the old pump stuck recently. It responded to a tap with my fist. The valves had grown a fair bit of crust on them too, so I knew they would be difficult to undo and clean up properly. When I got it all apart, the supply hole to the pump was almost closed off with a black crispy carbon like substance - hence the poor performance. I'll attach pictures. The question is :- what is the black crispy stuff, and how does it form, given that the drained off water was clear and the system has always been dosed with inhibitor? Has anybody seen it before and what can I do to prevent it happening again? Lastly, do you think any of the cleaning chemicals will remove it, or do I need to start replacing pipework and components as they fill up? Many thanks Les[​IMG]
  2. proff

    proff New Member

    The 'Black Crispy Stuff' is 'Magnetite' caused by 'Disimillar Metal Corrosion'.
    It should be greatly reduced by the use of an Inhibitor. I would just flush the system with a good cleansing agent as any sort of acid would be detrimental to the system and of little use against this. ;)
  3. tom.plum

    tom.plum Screwfix Select

    I've never seen a pump that badly made up, from where I'm sitting I'd say there'a a lot of lime scale mixed with that sludge, and thats unusual in central heating because the water that goes in the heating side is not renewed  and so there's only so much lime to give off, You'd expect to see that much on the domestic side where water is replenishing the cylinder all the time, I doult if chemicals will shift it, but its worth a try,
    I'd 'suck it and see' try x400 in it for a week, then strip it down and see if you're winning or not.
  4. Captain Leaky

    Captain Leaky New Member

    Very bad, and very unusual! I would physically strip and clean your system.
  5. Many thanks for your input. I have collected some of the black crispy stuff, scraped from the inside of the valves and pump. I tried it with a magnet and it sticks, but it wont stick to steel. So I guess it has a high ferrous content, but is not magnetised. The only sources of ferrous material are the radiators and iron heat exchanger in the boiler. So I reckon that's where it's come from, despite the inhibitor. I'll look at installing a magnetic based cleaning system to remove the metallic particles before they build up to cause a problem. Cheers Les

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