A dual fuel common rail system may be operated in a regular mode in which a relatively large charge of gaseous fuel is ignited by compression igniting a relatively small injection quantity of liquid diesel fuel. The dual fuel system may be operated in a single fuel limp home mode in which liquid diesel fuel is injected at higher pressures. Over pressurization of the gaseous fuel side of the fuel system due to leaked liquid fuel is avoided by regularly injecting leaked liquid fuel, but not gaseous fuel, from the gaseous nozzle outlet set during the limp home mode of operation.