Leaking Flue Gasses from a Contura 520 Stove

I've had my Contura for the last 9 years. It's been a very reliable and beautiful stove. The chimney is swept annually from the roof down, most recently last August. However I started to notice the strong smell of wood flue gasses in my lounge one evening in Mid November.

After extensive examination, trial and error, the source of the flue gas leak was not isolated, so I'm calling out to youtubers for advices.

My chimney sweep suggests the fact that I'm smelling flue gasses is most likely down to a partially blocked flue, since a good draw up the chimney is required to create a vacuum in the firebox. However this has been visually checked, see the video for evidence. There's no apparent blockage.

The smell is more noticeable when the firebox gets hotter and hotter, and it's not noticeable at all when the firebox is cold. Typically it starts to be noticed when the flue neck reaches 100 degrees C. Furthermore, I have made some very smokey kindling burns at low temperature, with air supply starved, and no visible smoke has been detected anywhere around the stove. This is very similar to a standard smoke bomb test that a qualified chimney sweep would perform.

Previously a chimney sweep came in and diagnosed quite a large gap between the flue collar and the stove, but that has since been sealed up with fire cement. This gap has been long standing, and wasn't new. Occasionally I would notice a puff of smoke if I closed the door on a cold stove.

As my sweep says, a negative gauge pressure in the flue means that smoke only comes out when the door is pumping the stove, or a back draught manifests itself in the chimney. In any case, it didn't solve the problem and I still have the smell of flue gasses.

Advice is required. I'm increasingly wandering if the smell is due to offgassing directly from the stove itself. This is a known issue for new stoves where volatile paint chemicals burn off on the first few operations. But I've not heard of anything like this for a 9 year old stove, and I've not heard of any offgassing that can specifically smell like flue gasses.

Видео Leaking Flue Gasses from a Contura 520 Stove канала Anthony Dyer