I have sprinkled talcum powder around the flue seal and inspection plate seal and started the boiler, during the initial ignition, a plume of talc rose into the air from the right hand side of the flu seal where it connects to the boiler top, so I am going to rake the old fire cement out down to the rope seal and repack with fresh cement. I am also going to tape up a flue joint as recommended by Boulter at the other end of the elbow where it joins the horizontal pipe through the wall, the installer has omitted the tape but I think I can see some kind of clear sealant in the join, I will tape it up anyway to be sure.