A fault location system for a telecommunications network including a local exchange or switch, a node such as a primary connection point and a plurality of line terminations to the customer includes probability calculation to establish the location of a fault measuring from the exchange. Historical non-faulty reference values of capacitance are compiled for each line passing through the node providing a measure of the distance of each line. A lowest valid capacitance value provides an estimate of the reference capacitance between the exchange and the node. Using various parameters, probability tables are compiled of historic fault values and a new fault is compared against these tables to establish the probability of it being a fault at the node or elsewhere. As a result the reference capacitance can be obtained without the need for an engineer at the node, and the likely location of a fault can be pinpointed with greater accuracy.