It's difficult to be completely certain from your image, but I would say it's a biscuit beetle Stegobium paniceum. This species has the honour of being the the most common enquiry seen by the ID team in the Museum!
The larvae like dried vegetable products like flour and spices and they are often found in kitchens. However if you suspect they are coming out of the chimney the source is likely to be an old bird or wasp nest or bread dropped down the chimney by birds. The best way to get rid of them is to find and remove the food source. If they are in your kitchen cupboards (or anyone else's) give the cupboards a scrub, throw away any old or infested food and keep open packets inside sealed tins, jars or plastic tubs.