A mass spectrometer comprising a control system arranged to assess an operational state of the mass spectrometer, wherein, when a fault is detected by the control system, the control system is arranged to assign the fault to one of a plurality of categories, wherein the categories include a first category of faults which may be attempted to be rectified automatically by the mass spectrometer, a second category of faults which may be attempted to be rectified by the user, and a third category of faults which may only be attempted to be rectified by a service engineer, the control system performing one or more steps based upon the assigned category of the fault; wherein when a fault is assigned to the first category of faults, the control system is arranged to proceed to initiate an attempt to automatically rectify the fault; wherein when a fault is assigned to the third category of faults, the control system is arranged to cause information relating to the fault to be displayed to the user, the information comprising data indicative of the fault, and an indication that the user should call a service engineer; wherein, when a fault is assigned to the second category of faults, the control system is arranged to cause information relating to the fault to be displayed to the user, the information comprising data indicative of the fault and data indicative of one or more steps to be taken by the user to attempt to rectify the fault; wherein the control system is arranged to perform one or more tests to determine whether the fault has been rectified once the user has attempted to rectify a fault, once an indication has been received from the user that they have attempted to rectify the fault; wherein the control system is arranged, when it is determined that a fault has not been rectified after a permitted number of attempts by a user, to reassign the fault to a category of faults which may only be attempted to be rectified by a service engineer; and wherein the mass spectrometer is configured to store data indicative of possible faults and the category to which such faults should be assigned, for use by the control system in assigning a fault to one of the plurality of categories. wherein when a fault is assigned to the first category of faults, the control system is arranged to proceed to initiate an attempt to automatically rectify the fault; wherein when a fault is assigned to the third category of faults, the control system is arranged to cause information relating to the fault to be displayed to the user, the information comprising data indicative of the fault, and an indication that the user should call a service engineer; wherein, when a fault is assigned to the second category of faults, the control system is arranged to cause information relating to the fault to be displayed to the user, the information comprising data indicative of the fault and data indicative of one or more steps to be taken by the user to attempt to rectify the fault; wherein the control system is arranged to perform one or more tests to determine whether the fault has been rectified once the user has attempted to rectify a fault, once an indication has been received from the user that they have attempted to rectify the fault; wherein the control system is arranged, when it is determined that a fault has not been rectified after a permitted number of attempts by a user, to reassign the fault to a category of faults which may only be attempted to be rectified by a service engineer; and wherein the mass spectrometer is configured to store data indicative of possible faults and the category to which such faults should be assigned, for use by the control system in assigning a fault to one of the plurality of categories. <EOS>