A method of controlling pressure maintenance equipment for a cooling and heating system, the pressure maintenance equipment comprising: a first expansion tank and a second expansion tank both provided branching off from a circulation piping system having pipe water therein, and connected parallel to the circulation piping system, the first expansion tank and second expansion tank being connected to each other by an equalizing pipe; a first pressure sensor and a second pressure sensor respectively and independently provided on the first expansion tank and the second expansion tank, each of the first and second pressure sensors (P1, P2) measuring an internal pressure of the corresponding expansion tank; a third pressure sensor sensing a pipe pressure of the circulation piping system; a nitrogen supply unit supplying nitrogen gas into the expansion tanks (130, 130'); nitrogen gas supply valves provided to supply nitrogen gas from the nitrogen supply unit into the corresponding expansion tanks; and nitrogen gas exhaust valves provided to exhaust nitrogen gas from the corresponding expansion tanks, the method comprising: measuring the internal pressure of the first expansion tank using the first pressure sensor; measuring the internal pressure of the second expansion tank using the second pressure sensor; measuring the pipe pressure of the circulation piping system using the third pressure sensor; calculating absolute values of differences among measurement values of the internal pressures of the first and second expansions tanks (130, 130') and a measurement value of the pipe pressure of the circulation piping system, measured by the corresponding pressure sensors (P1, P2, P3), and calculating measurement deviation values between the respective pressure sensors (P1, P2, P3); comparing the calculated measurement deviation values between the respective pressure sensors (P1, P2, P3)with a preset deviation value; determining whether an abnormality has occurred in each of the pressure sensors (P1, P2, P3)based on the result of the comparison between the measurement deviation values and the preset deviation value; excluding the measurement value of a pressure sensor that is determined to be abnormal and the measurement value of the third pressure sensor, and outputting the measurement value of the remaining pressure sensor or a mean of the measurement values of the remaining pressure sensors (P1, P2) as a reference control value for the internal pressures of the expansion tanks (130, 130'); and comparing the output reference control value with a preset target reference value of the expansion tanks (130, 130'), and based on this comparison, determining whether the pipe water has expanded or contracted, and supplying nitrogen gas to the expansion tanks (130, 130') or exhausting nitrogen gas from the expansion tanks (130, 130') depending on a result of the determining whether the pipe water has expanded or contracted. measuring the internal pressure of the first expansion tank using the first pressure sensor; measuring the internal pressure of the second expansion tank using the second pressure sensor; measuring the pipe pressure of the circulation piping system using the third pressure sensor; calculating absolute values of differences among measurement values of the internal pressures of the first and second expansions tanks (130, 130') and a measurement value of the pipe pressure of the circulation piping system, measured by the corresponding pressure sensors (P1, P2, P3), and calculating measurement deviation values between the respective pressure sensors (P1, P2, P3); comparing the calculated measurement deviation values between the respective pressure sensors (P1, P2, P3)with a preset deviation value; determining whether an abnormality has occurred in each of the pressure sensors (P1, P2, P3)based on the result of the comparison between the measurement deviation values and the preset deviation value; excluding the measurement value of a pressure sensor that is determined to be abnormal and the measurement value of the third pressure sensor, and outputting the measurement value of the remaining pressure sensor or a mean of the measurement values of the remaining pressure sensors (P1, P2) as a reference control value for the internal pressures of the expansion tanks (130, 130'); and comparing the output reference control value with a preset target reference value of the expansion tanks (130, 130'), and based on this comparison, determining whether the pipe water has expanded or contracted, and supplying nitrogen gas to the expansion tanks (130, 130') or exhausting nitrogen gas from the expansion tanks (130, 130') depending on a result of the determining whether the pipe water has expanded or contracted.