Collect the clues
Record the zone number, controller model and any displayed error. Note whether the problem is consistent or intermittent and whether wiring or landscaping work happened nearby. Do not open electrical enclosures or probe wiring.
How the assessment differs
The technician may need to distinguish controller output, field wiring and valve operation. Ask what testing supports the proposed repair. A new controller will not correct a disconnected field wire or a mechanically stuck valve.
Compare the scope
A quote should identify the failed component or explain what remains uncertain. Ask whether diagnosis, replacement parts, programming and a zone test are included. Buried wiring faults may require a different visit or additional access.
Useful question
Can the technician document which component failed rather than replacing several possibilities at once?