There is a hairline plaster crack where the chimney runs behind a plastered wall (I assume originally caused by heat from the chimney) and when the fire is on (woodburner) the wall obviously heats up slightly and the crack expands. When it cools it contracts again and is almost unnoticable.
I want to wallpaper this wall but if I do I think the paper will just split/tear. The crack has been filled with standard filler previously but just cracks again. Would filling with flexible filler work and if so can you recommend one? Any other advice to try?