A liquid circuit for filtering a liquid, comprising a liquid storage vessel (10), a liquid pump (17), a consumer or user device (14), a filter element (23) and a controller (24). A heated liquid can be supplied at least partly to the filter element (23). The liquid circuit may be used in liquid systems in which a liquid, such as water, oil or fuel, is filtered and at least part of the liquid is returned to the storage vessel (10). The liquid is pumped in the liquid circuit from the storage vessel (10) by the pump (17) through lines (11, 13, 15, 16), filtered by filter element (23) and supplied to the consumer device (14). Excess liquid not required by the consumer device (14) is returned through liquid return line (15) to the controller (24) which directs the liquid either to the filter element (23) or the storage vessel (10), depending on the liquid temperature. The controller (24) and the filter element (23) are arranged in a common housing (18) having connectors for an unfiltered liquid inlet (19), a filtered liquid outlet (20), a liquid return (21) and a liquid outlet (22). The connectors (19, 20, 21) fixed to the housing enable rapid and simple assembly of the liquid circuit.