Nine real diagnostic scenarios in a Symptoms → Diagnosis → Testing → Resolution format — chronic low pressure, recurring drain clogs, sewer gas odor, water hammer, scalding risk, grease interceptor overflow, backflow preventer test failures, simultaneous-demand pressure drop, and a failed hot water recirculation loop.
Replacing a part and hoping a complaint doesn't come back is a service call, not an engineering diagnosis — it treats the symptom as the problem. This module builds the measure-first discipline that separates a defensible diagnosis from a guess: nine real scenarios, each with at least two plausible causes that present nearly identically, worked through in a consistent Symptoms → Diagnosis → Testing → Resolution format so the specific field measurement that actually distinguishes the causes is never skipped.
By the end of this module you should be able to explain why a frozen coil, a dry trap, or a failed mixing valve each have at least two structurally different root causes that look identical at the fixture — and why Module 16's commissioning records are frequently the first document a real diagnosis reaches for.