Safety Device The limit switch is a very important safety device on the furnace that prevents the furnace from overheating. Therefore, when a limit switch has been used for a long time or is obviously broken, it should be replaced with a new one for security. Perfect Fitment 2 Pack Limit Switch, Fits for Atwood Hydroflame RV Furnaces. Compatible with 1522 2 STAGE, 1522 LD 2 STAGE, 2334 2 Stage, 8516-III, 8516-IV, 8520-III, 8520-IV, 8525-III, 8525-IV, 8531-III, 8531-IV, 8535-III, 8535-IV Models. High Quality .