Blocked overflow pipe — Opal rad.

[stuartu]

Would a piece of Bowden inner cable be any more amenable, Charles? A fairly short piece to start with or the drill will just tie it in a knot.

Vinegar will dissolve the carbonate eventually if you can get some in there in due course.

Regards,

Stuart

Edited to add, as plan B I agree with Hedd. If you don't fancy attempting it yourself I would hope your local radiator people wouldn't charge a packet to do the job.