There probably isn't anything wrong with your kiln. Kilns lose heat out the floor and lid. The sitter only measures heat work in the middle of the kiln. There will always be inconsistent heating throughout the kiln, so you have to load it in a way that deals with that. If an area is running cold, pack it looser there. If it's running hot in a specific area then pack it tighter there. If you can get the whole thing within 1/2 a cone then you're good.
- Mark (Marko) Madrazo likes this