Boiler bumping & banging

I have had a problem with a bumping central heating boiler for some time. Sludge removers and descailers in vast quantities and lengthy flushing sessions with a hosepipe connected to the water main have failed to stop it.
Today I drained enough water off to empty the F&E tank with all the rad bleed valves closed, which probably caused water to flow through the boiler in the reverse direction. It was clear at first and then turned a very dense light brown colour. Going up to the now near empty F&E tank, in the bottom it had a thick slimy light brown sludge mixed with white flakes, which I cleaned out. On refilling and firing up the boiler again the bumping was dramatically reduced but began to increase a little after a few hours.
I think this must be a biological growth of some kind getting into the boiler. Can any of you kind people tell me something more certain about this and how to clear it from the system? It has been flushed and refilled with X100 added several times over the last three years, the boiler is three years old (Glow Worm Ultimate). The F&E tank has been lacking a lid.
Thanks for any help,
Eric
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gnome wrote:

Sounds to me more like hardness scale from the water. Are you in a hardwater area? All these descaling agent should not be necessary in such a newish system. I didn't have to descale my system until it was at least 10years old. afaik these chemicals are acid so you are probably eating your system away. My boiler kettling was eventually cured by fitting a pump that was man enough for the job..
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wrote:

Don't be too sure... Did you never see Quatermass and the Pit?
.andy
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You must be near my age, God help you. <g>
Eric
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wrote:

Not that you have them but thermophilic bacteria can and do live in conditions much harsher than your boiler can muster.
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A biological gunge can form in the F&E tank and grow very happily in the warm condiditons there. No doubt it will die in the boiler but its sludgy remains, I am told, can cause significan problems!! [...]

My pump is a MAN'S pump - I can assure you.
Eric
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several years ago. Dad said it was an old way to get rid of it, stopped it in about 1 minute. i don;t know why/how it should work, and it didn't seem to have any negative effects by addition.
maybe the boilermen can give a reason why it did it, and also mostr likely tell you why you shouldn't do it ;)
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On Sat, 08 Nov 2003 18:01:10 +0000, David Hemmings

When used for washing up, dishwashing liquid reduces the surface tension of the water. I would imagine that in the application you describe it would stop formation of large steam bubbles.
However, there is a downside. It contains a lot of salt, so you wouldn't want to use much.
One of the chemicals specifically for this purpose, e.g. from Fernox or Sentinel would probably be a safer option.
.andy
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">

Salt!!! How much salt is a dash of washing up liquid going to contain???? And I doubt the accuracy of this anyway.
Eric
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wrote:

I will know if there is a next time and get my arse down to the plumbing shop :)
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