Thanks for the reply mate. To my ears it actually sounds like an old Geiger counter off the telly.
I did drain down the system as part of the DS40 treatment and flushed it through until it ran clear. When draining some off it's a greeny yellow colour and is foamy on top.
I should mention...
Hi everyone. I'm a long time lurker, first timer poster.
In our house we have a Linea 726 combi boiler. Its 6 years old. Over the last year it has become noisy and I've had an engineer service it in the last couple of months.
Initially having read various things about kettling I had...