This second in a series of “mysteries” from American Control & Engineering Service Inc., Rose Hill, Kan., exposes why a paint-bake oven for a plating company would quit burning at random. In addition, the sensor in the flame rod reported no contact with fire.

After examining the clues, the ACES pro on the case replaced an old flame relay. But alas, that didn’t solve the problem. Next, he changed the wiring between the flame rod and flame relay. However, that wasn’t a permanent solution either. Finally, the ACES “detective” disassembled the burner and discovered a warped burner tube, which could have lead to a situation in which the flame became instable and lifted away from the flame rod. Unfortunately, the burner tube was a $500 custom part with a 10-week lead time.

The main culprit for the unexplained outages, though, was the unstable flame. Whether caused by the warped burner or something else, the flame varied enough to stray outside the range of the flame rod’s sensor.

No one wanted a cold case, so ACES replaced the flame rod with an ultraviolet sensor. Instead of replacing the burner tube -- an expensive custom part -- ACES installed a $100 part that works fine in the unstable flame environment. Now the paint bake oven burns consistently with no interruptions.

Case closed.