The mild steel collar between the wood-burning stove and stainless steel flue split at the back (hidden from view of course) and some of it was lost through rust. A chimney leak a few years ago had allowed rain to trickle down to the stove, and I guess was enough to rust and weaken the collar.
Dealing with the split and lost metal was a bit of an issue. The collar did not appear on the stove spare parts list, and a previous repair to the stove outlet pipe had required the services of a HETAS engineer. It wasn't cheap. There was no way I was going to change the collar, so decided to repair it with fire cement, and got a 1kg tub from B&Q. I'd checked the info at
It was only when I read the label small print after purchase did I find out that it was not suitable for repairing metal! I wonder how many "internal flue pipes" are not made from metal. The technical info available at the Bostik website states: "Bostik Fire Cement is suitable for repairs to a wide range of applications where heat resistance is required, including fire backs, chimney linings, solid fuel heaters, broken bricks in grates & stoves, boilers and other surfaces which may be exposed to extreme heat and are not made of metal or plastic."
What nonsense! Are there many surfaces which may be exposed to extreme heat and are made of plastic?! It also adds "Do not use in metal joints due to movement & vibration". Despite this, I decided to use it, but reinforce it somehow which would help prevent bits cracking off with expansion movement. I used a small amount of rockwool insulation from the loft, and mixed it in with the cement. This was then smeared liberally over the SS flue pipe beneath the crack. I opened the steel collar crack some more and jammed in more of the cement/rockwool material. Finally, I fitted a couple of 115 - 140mm SS jubilee clips over the cracked collar and tightened them until the collar was back in position. This forced out a lot of the cement, but I used it to build up a layer over the collar split. This was allowed to dry for 24 hours, and then I lit the fire. That was yesterday and so far all seems ok.