Symptom, cause, action

Every good fault description answers three questions in order.

What did you observe? Measurable, with a tag and a number. "FT-4210 indicated 0 flow while the pump was running and discharge pressure was normal."

What caused it? If you know, say so plainly. If you do not, say what you ruled out. "The transmitter had failed low. The pump and the line were confirmed healthy."

What did you do? Past simple, specific. "We replaced the transmitter, carried out a loop check and returned the instrument to service at 09:40."

Avoid "the pump was not working". It tells the reader nothing they can act on, and in a joint-venture review it will always come back as a question.