increasing boiler kettling noise

We recently (about 2 months ago) had a Keston Celsius 25 boiler installed, and it's been great. However, it is now making some kettling noises which it wasn't when first installed, which seem to be getting louder as the days go by. Nothing's changed, except the weather has got colder and so it is running more. I posted a while ago about a sort of "chuffing" noise it was making, this noise seems to be caused by kettling.
I thought that as the air was driven out of the new water in the CH loop after installation, the kettling should get less rather than more. There's no air in the system now as far as I can tell, every bleed point just produces water. Would it be worth trying some Fernox anti kettling stuff or is that a waste of time.
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Tim Mitchell

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Kettling is often caused by poor flow. Try to eliminate anything that might restrict the flow of water. (i.e. air locks, sludge, faulty pump, faulty zone valves, closed off or missing bypass).
Christian.
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