On Monday Evening 2/11/19, a homeowner called the station and advised his ceilings were getting unusually hot to the touch. The Box assignment was initiated and Engine 6-1, Trk-6 responded with mutual aid companies. Crews found the issue to be in an upstairs bathroom ceiling of an early 1900 residence. unable to determine what was causing the heat, and the TIC picking up heat the decision was made to open the ceilings. What the crews found was a very old radiant ceiling heating system that was failing. Thanks to the diligence of the crew in not giving up and finding the root of the issue. YOU NEVER KNOW WHAT YOU'R GOING TO RUN INTO.