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