Is it safe to mount a large TV on my chimney breast? What should I check first?

Mounting a TV on a chimney breast isn't always straightforward. First, confirm if the chimney is active. Active chimneys generate heat, which is bad for electronics and can be a fire hazard. Second, you need to know what the chimney breast is actually made of. Many are solid brick, but some are decorative façades over a framed wall. Drilling into a flue or compromising the chimney structure is dangerous. Use appropriate masonry anchors if it's solid brick, or find studs if it's a framed wall. If in doubt, have a qualified professional, like a chimney sweep or a structural engineer, assess the structure and heat output before you hang anything heavy there.