Noisy Boiler

I have a 10 year old Halstead 55FF boiler which when in CH mode is noisy.
The noise starts about 30 seconds or so before the thermostat trips out the burner.
This only occurs when the system is up to temperature i.e. radiators are hot.
After the burner shuts down the noise subsides until the same point in the next cycle.

The noise is similar to that of a jet aircraft flying overhead.
If I turn the boiler 'stat down to about 3 the noise does not happen.

From reading the other postings I guess that the system needs desludging and flushing.
If this is the case can anyone please recommend products for this task.

Thanks

Well done for doing the research. I think you're right in suspecting sludge in boiler, probably in main heat exchanger. However check that there aren't any filters fitted on the return pipe. These could block and prevent circulation. Also check if there is a by-pass, either internal or external. This will help to determine where blockage is.

As for flushing treatment, there are various methods and chemicals. I'm sure some more research will bear fruit. Personally I would try flushing using mains pressure water, but you have to set up suitable fill and discharge points (and have a logical mind) to make the most of this method.