Do you have standard diagnostics and troubleshooting procedures that lead logically to repair recommendations? If not, you’re relying on custom troubleshooting. When custom troubleshooting can’t be avoided, a tech with formal training in troubleshooting can efficiently determine what’s wrong and probably figure out how to fix it.
For critical equipment, relying on custom troubleshooting leaves too much to chance. It’s unlikely your ace tech(s) will always be available to respond when critical equipment goes down. What happens when only techs who aren’t familiar with that equipment are available? And pressure is high to fix it now? You get guesswork.
The knowledge of how to determine what’s wrong and fix it should be embedded into procedures. Ideally, the diagnostic steps will be in flowchart form with decision boxes. A tech should be able to proceed quickly from one diagnostic to the next, until arriving at “Do this to fix the problem.”