1. Method for monitoring the condition of a valve and valve operator to signal a need for maintenance of the valve or valve operator, said method comprising the steps of: determining a minimum operator thrust required to close the valve; determining a maximum thrust deliverable by the valve operator before operator motor shut down; imposing a load in the valve operator during a calibration period to generate a control thrust equal to the difference between the said maximum thrust and said minimum thrust; measuring a power parameter associated with the valve operator in response to the operator having generated said control thrust to acquire a control value for the power parameter; ending the imposing of a load in the valve operator during the calibration period; placing the valve operator in use; and monitoring the said power parameter while the valve operator is in use to acquire actual values of the power parameter; whereby an actual value in excess of the control value indicates an inability of the operator to generate the determined minimum thrust and thus inability to open or close the related valve.