Today I

Fernoxed.

And after work, too. Boiler noise came back a few weeks ago so we persuaded our plumber to drop off some silencer, as it's only a matter of months since we had the system flushed. We've been putting off the job but finally decided to tackle it today. Worked out how to drain off some water then went to the header tank to discover a thick layer of slime covering black particled water. So I got a bucket and cleaned. And cleaned. And cleaned. Then flushed through and added the magic. And guess what- so far, no boiler noise! But now I wonder if I should add some more inhibitor, as we've basically refilled the system. Any plumbers out there?