The printer queue that sticks every Friday
Every Friday the printer queue sticks. Each time, a technician clears it and the printing works again.
Clearing the queue treats a symptom. The real reason is still there, so it sticks again next week. To stop it for good, you must find the root cause.
By the end of this lesson
Note
I can use a root cause method to find the real reason for a fault and say what to do next.
Key words
| Word | What it means |
|---|---|
| Symptom | What you can see going wrong |
| Root cause | The real reason a fault happens |
| Five whys | Asking "why?" again and again until you reach the root cause |
| FMEA | A table that lists how things could fail and scores each one |
| Event tree | A diagram that follows one event through safety steps that work or fail |
| Log | Write down what happened and what was done |
| Escalate | Pass a problem to somebody with more skill or authority |
The cells students fill in are left blank in this preview.
Starter
Have a go
Starter
3 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.
A root cause stops a fault coming back
The purpose of root cause analysis is to find the real reason for a fault, so the fault does not return.
Use it when a fault repeats, when it is serious, or when a fix only hides it. A quick fix is fine for a one-off. A root cause is needed for the Friday queue.
Method one: the five whys
Ask "why?" about the symptom. Then ask "why?" about the answer. Keep going, about five times, until you reach a cause you can fix.
It is fast and needs no tools. It works well for faults with one chain of causes.
Five whys: the Friday queue
| Question | Answer |
|---|---|
| Why does the queue stick? | A print job is stuck |
| Why is the job stuck? | The print service stopped |
| Why did it stop? | It ran out of disk space |
| Why is the disk full? | Old logs are never deleted |
| Why are they never deleted? | Nobody set a clean-up job. This is the root cause. |
The cells students fill in are left blank in this preview.
Check
Have a go
Check
3 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.