Part 3 – Intermittent and Recurring Problems

3 people talking in factory

Have you ever attempted to solve a problem for which symptoms appeared, disappeared, and reappeared again? This scenario is referred to as an intermittent problem, and it can be fairly frustrating to recognize and solve.

To find the root cause(s), you must determine the timing of the symptoms. Here are the six steps to deal with this type of challenge:

  1. Document each time the symptom(s) appear and disappear. Record specific dates and times, including when the symptoms began and ended.
  2. Document all changes that occur prior to and immediately after the onset of the symptoms. Operator shifts, environmental conditions (e.g., temperatures, humidity), operating speeds, and material changes are all examples of potentially useful clues.
  3. Create a simple time-based run chart depicting start and stop times for each occurrence of the symptom(s).
  4. Transpose the documented changes directly onto the run chart at the appropriate date and time coordinates.
  5. Look for a correlation between the documented changes and the date/time that the symptoms occurred.
  6. Analyze the plotted results. Is there a repeating pattern? That is, do the symptoms occur at the same time every day? Is the pattern periodic? Is the pattern cyclical?

Recurring problems

Once in a while, when a piece of equipment has supposedly been repaired, the same problem recurs with precisely the same symptoms it had before. Recurring problems are always the direct result of inadequate or incomplete problem-solving techniques applied in the first attempt at a solution. Problems typically recur for one of these reasons:

  1. The root cause of the problem was not previously found; therefore, only a symptom was treated.
  2. The repair was inadequate or incomplete.
  3. The diagnosis was made incorrectly, based on insufficient or inadequate information.
  4. The root cause was deliberately avoided. Sometimes people avoid problems they don’t know how to solve or repairs they don’t know how to make. Even worse, sometimes people are too tired or disinterested to work conscientiously.
  5. The repair was cost or time prohibitive, so a temporary, cheaper, or quicker repair was made instead. Shortcuts almost always cost more time and money in the long run.

Problem Solving Traps to Avoid

Even when we have the best fundamentals, processes, and tools at our disposal, problem-solving does not always go according to plan. Often, obstacles get in the way, or an unexpected variable diverts the problem-solver on a wild goose chase. I refer to these as “problem-solving traps.” Since you can’t eliminate them from your future challenges, it pays to become aware of the most typical types of traps, and what you can do to mitigate their risks:

  1. Erroneous information, facts, or data supplied by someone else involved. Misinformation can be supplied deliberately in an attempt to sabotage the process for personal gain (e.g., to get time off for equipment downtime). It can also be supplied unintentionally by someone just trying to be helpful, who doesn’t understand the value of accurate information. Be wary of generalized statements such as “It’s always been like this” or “I think it happened last week.” Be even more dubious about emotionally charged or hyperbolic statements like “This piece of garbage always screws things up!” Whenever you’re in doubt, collect new data or seek new information from other sources.
  2. Defective parts, measurement tools or gauges. As trusting people, we may assume that if we install a part, that it must be functional and that all gauges and tools work properly. This is not always the case. If you are reasonably certain that a part is defective, and you install a replacement that doesn’t fix the problem or if you are getting readouts that are too high or low, do more testing.
  3. Defective input material. Out-of-spec raw material can create a trap. Raw material characteristics that affect the final product can lead you to the wrong conclusions. For example, if the viscosity of a material is outside of the acceptable range, the material will exhibit different flow properties inside the mold. Wrong assumptions about defective input materials will lead to a defective end product. When in doubt, retest!
  4. Incorrect drawings or schematics. How often have modifications been made to your equipment without a corresponding update to the related drawings or schematics? Even subtle changes to the process wiring or hydraulics must be added to the drawings in a timely manner. Without these updates, drawings and schematics become a trap for future problem solvers.
  5. Incorrect logic on your part. Even if you have undergone a thorough problem-solving process, it is still possible that some of your premises or assumptions could be erroneous. That is why it is good practice to have someone review your thoughts and conclusions. Far from being a sign of weakness, involving someone else in a review shows foresight.

In the next post, we'll discuss two key problem solving tools that use cause and effect diagrams and causal chains.

Bob Sproul

About the Author

Bob Sproul helps businesses across the manufacturing spectrum improve their operations for more than 40 years.