In the Field · Part 4

The diagnostic method: verify, isolate, cheapest test first, cause not symptom, the options ladder, document

A plumber who has passed the exam knows the code. A plumber who runs a business needs one method that turns any call into a finding, a set of priced options, and a paper trail, the same way every time, whether the call is a hissing wall or a heater that failed inspection. This lesson is that method in six steps: verify what the customer actually observed, isolate which system it belongs to, run the cheapest test that can rule something out, keep going until you have the cause rather than the symptom, present an options ladder with a cost band, a permit path, and a code section for each rung, and document it so the next person, or the investigator, can follow it. Every domain lesson in this phase applies it; the cases show it deciding outcomes.