On 24/12/2020 10:21, alan_m wrote:
On 23/12/2020 11:48, wrote:

Thanks, but I'd ruled-out a DIY version of those because of the
problems of storing a big sooty thing, and crud falling down when it's
pulled from the chimney

Irrespective of any mode of blocking you are going to get the crud that
has fallen on the blocking mechanism dropping down when opening up
again, otherwise where do you expect this crud to disappear to?

Even with a bespoke fixed design consider how it is to be cleaned.


An angle-iron frame around the outside with a pivoting, removable and
counterbalanced plate that fits into the frame.