Here's what the tiles in a chimney flue look like when they need to be scraped off and the flue needs to be relined. You're probably thinking this is an old home and that might not be so unusual. Well, it's my home that was built in 2017. In other words, no matter what age the home is, it's a good idea to get a full chimney inspection. That means that the chimney inspector will insert a camera all the way up to the top of the flue. The inspector is looking for missing mortar between the tiles and other issues that can be a fire hazard. The subcontractor who installed my chimney flue 4 years ago did a really poor job and it was good that I had it inspected and caught the problem before a possible fire. It's now lined with a corrugated steel liner that's guaranteed for life. Oh, and one other thing. The company that did the replacement is MCP Chimney & Masonry in Damascus, MD at facebook.com/mcpchimney or https://mcpchimneyservices.com/ . They not only did a great job, they also left the room spotless and their pricing is very reasonable.
I always recommend a chimney inspection to my buyers. Call me at 240-234-1000 or email me at email@example.com with any of your real estate needs in MD, DC or VA.