Dear Mr Hayes,
I had a massive extension done on my house over the summer. CH was drained down and refilled a couple of times over the three month period. I had already bought some "Protex" CH system Protector, but didn't want to add it until I had added a conservatory radiator, some 4 months after the first drain down.
Was woken one morning at 04:30 by steam train sounds, accompanied by popping and banging - "Kettling" described the sound perfectly.
Shut off the header tank supply, drained down a couple of gallons, then fed my Protex directly into the header tank line.
Went away for a couple of days, and on my return, most of the kettling had gone.
A month or so later, drained system down - added radiator, then added "Scalex" and "Protex" and refilled system. It runs like a dream now
with no noise.
The "Protex" in an inhibitor, "Scalex" is a descaler that does not require flushing out. If the system is really bad, then you could try "Flushex" first (fill, run & drain) then the other fluids.
A word of caution when using "Flushing" fluids. My brothers flat had a radiator which would not come on. We suspected a blockage, so flushed system through. Next day, the hot water tank coils started leaking CH water into the hot water tank, and a month later, the flat below reported "light rain" from the ceiling - a joint below the floor had let go!
Paul