Glow-Worm Fuelsaver 55F. Very noisy boiler?

Glow-Worm Fuelsaver 55F. Very noisy boiler.

Although this boiler is of the ancient variety it is however still working perfectly. The problem lies with the initial boiling process being extremely noisy. Unfortunately the instruction manual is of little use. I am led to believe that in most cases this noise is due to air trapped within the exchanger system. This could be true as I have drained and re-filled the system fairly recently due to adding extra pipework and radiator to the system. (Although it has taken some time to get to this noisy stage?) I have bled the exchanger twice with no better results. Could there also be solder remnants stuck in this part of the system that are being churned around making this noise. If so then will I need to strip the exchanger out to clean these deposits out?
Many thanks for your help.
Rich Stevens