Documenting an Unsolved Fault for the Next Tech

Why this matters

When you leave a job without solving it, your notes are the only thing the next visit inherits. Good notes mean the next tech, often you on a return trip, picks up where you stopped. Bad notes, or none, mean the whole diagnostic starts over: the same tests, the same dead ends, the same hour burned, on the customer's clock and your reputation. "It was acting up, could not find it" is not documentation, it is an apology. This is how to write a handoff that actually moves the diagnosis forward.

Step 1: Record the complaint in the customer's words and yours

Start with what is actually wrong, from both angles.

• The customer's complaint, verbatim: what they reported, when it started, how often, under what conditions. Their words carry clues your tests might miss ("only on the hottest days," "after it has run a while").
• Your translation: what that complaint means in technical terms, so the next tech is not guessing at the customer's phrasing.

Both matter. The customer describes the symptom they live with; you describe the fault you are hunting.

Step 2: Write down what you observed and measured, with numbers

This is the heart of the handoff. Vague observations are useless; specific readings are gold.

• Record actual values, not impressions. "Pressure low" tells the next tech nothing. The actual reading, the expected range, and where you measured it tells them everything.
• Note the conditions when you measured: running or off, cold or warm, load state, ambient. A reading without its conditions cannot be compared.
• Capture any fault codes or indicator patterns exactly, and whether they were active or stored. Record them before clearing. See the related fault-indication reference.
• Photograph the evidence: the corrosion, the burn mark, the gauge reading, the panel. A photo survives where memory fails.

The single most valuable thing you can leave is a set of baseline readings, because a progressive fault is only visible by comparing your numbers to the next visit's.

Step 3: List what you ruled out, and how

The next tech needs to know where not to spend time. An unsolved fault with a clear "already eliminated" list is half-diagnosed.

• Name each thing you tested and cleared, with the evidence. "Checked the X, measured normal, ruled out" saves the next person from repeating it.
• Be honest about what you did not test and why (no time, no tool, no access). A gap you flag is a gap the next tech can close; one you hide, they rediscover.

A ruled-out list is what separates a real diagnostic handoff from a fresh start. It is also what stops the next tech from wasting the visit re-confirming what you already know.

Step 4: State your leading theory and what would confirm it

You almost always leave with a hunch, even an unproven one. Write it down as a theory, clearly labeled as not yet confirmed.

• Your best current theory of the cause, and the reasoning behind it.
• What test or condition would confirm or kill it. This points the next visit straight at the deciding step.
• What you would do next if you had the part, tool, time, or access you lacked.

Label it a theory, not a conclusion. A clearly-marked hunch helps; a guess dressed as a finding sends the next tech down your wrong path with false confidence.

Step 5: Note the state you left the equipment in

The next tech needs to know exactly what they are walking into.

• Running, off, or tagged out, and why. If you red-tagged it for a safety reason, say what and why in plain terms.
• Anything you changed, disconnected, or left mid-repair. A wire you lifted, a panel you left open, a valve you closed. An undocumented change is a trap.
• Any monitoring you left in place and what it should capture.

Step 6: Give the customer their part of the job

If the fault is intermittent, the customer is your sensor between visits. Tell them, in writing, exactly what to capture.

• Specific, not vague: "Write down the time and what the unit was doing each time it happens," not "let us know if it acts up."
• What to note: time, conditions, any sound, smell, or display at the moment.
• What to do if it becomes a hazard: when to shut it off and call right away.

The handoff test

Before you close the job, read your notes as if you were a tech who has never seen this unit. Could you walk in, know the complaint, know what was measured and ruled out, know the leading theory, know the next step, and know the equipment's state, without calling the person who wrote it? If yes, it is a handoff. If you would have to phone the previous tech to understand it, it is not done yet.

References

• Trade-standard practice for service documentation and diagnostic handoff
• Manufacturer documentation for recording fault codes and baseline readings
• See related: Reading an Error or Fault Indication (reference); The Diagnostic You Can't Finish On Site (decision tree); The Fault That Comes Back Bigger (decision tree)