I must be honest, If I said to my client, I'm just going to poke it with a stick and see if I can free things up, I'd quite rightly be shown the door.
I originally asked the OP, on the first page of that post, if a magnet was being attracted to that area, he said it did, there's the evidence. That is a well established test to identify that there is a significant amount of magnetite at the CC area of the feed and vent. If there is enough magentite to attract a magnet then there it points to a significant, if not total blockage in that area. If it is blocked to that degree then invariably it will need cut out as it will be solid, that is a well known and accepted industry standard fix. It is very unlikely this type of blockage could be removed by any mechanical or other means and the safest way to remove it is by cutting it out and then cutting back until the pipe is clear. That's what experience tells me would be the first course of action.
It is a relative quick and easy repair and could even be performed by a competent DIY'er using a pipe slice, some copper pipe and compression fittings, if that's what was ultimately preferred.
The system would then be looked at to see what else may be recommended to prevent it happening again.
TBH, this could have all been done and dusted really quickly instead of running into pages and pages of wrangling.
