A central tyre inflation system for a vehicle comprising: a plurality of inflation control valves for controlling inflation of a respective tyre; and a first gas source for supplying pressurised gas to the inflation control valves, the system further comprising a first gas inlet valve (VIN1, VIN2) for controlling the supply of gas from the first gas source to a fluid gallery, the system comprising a plurality of gallery outlet valves each arranged to control gas flow between the fluid gallery and a respective tyre supply line, each tyre supply line being provided in fluid communication with the inflation control valve of a respective tyre and arranged to supply gas from the fluid gallery to the inflation control valve, the gallery being provided with an exhaust valve for exhausting gas therein, characterised by at least two gallery pressure sensors (35A, 35B) for measuring a pressure of gas in the gallery, at least one electronic controller being configured to perform at least one system check comprising a gallery pressure sensor check, the gallery pressure sensor check comprising, with the gallery outlet valves and first gas inlet valve (VIN1, VIN2) closed, causing the gallery exhaust valve to open and monitoring the pressure in the gallery according to each of the at least two gallery pressure sensors (35A, 35B), wherein if the pressure in the gallery according to the at least two gallery pressure sensors (35A, 35B) does not correspond substantially to a predetermined datum pressure, the electronic controller determines that the system has failed the system check, wherein if the control means determines that the system has failed a system check the electronic controller is configured not to permit inflation or deflation of one or more tyres by the system. a plurality of inflation control valves for controlling inflation of a respective tyre; and a first gas source for supplying pressurised gas to the inflation control valves, the system further comprising a first gas inlet valve (VIN1, VIN2) for controlling the supply of gas from the first gas source to a fluid gallery, the system comprising a plurality of gallery outlet valves each arranged to control gas flow between the fluid gallery and a respective tyre supply line, each tyre supply line being provided in fluid communication with the inflation control valve of a respective tyre and arranged to supply gas from the fluid gallery to the inflation control valve, the gallery being provided with an exhaust valve for exhausting gas therein, characterised by at least two gallery pressure sensors (35A, 35B) for measuring a pressure of gas in the gallery, at least one electronic controller being configured to perform at least one system check comprising a gallery pressure sensor check, the gallery pressure sensor check comprising, with the gallery outlet valves and first gas inlet valve (VIN1, VIN2) closed, causing the gallery exhaust valve to open and monitoring the pressure in the gallery according to each of the at least two gallery pressure sensors (35A, 35B), wherein if the pressure in the gallery according to the at least two gallery pressure sensors (35A, 35B) does not correspond substantially to a predetermined datum pressure, the electronic controller determines that the system has failed the system check, wherein if the control means determines that the system has failed a system check the electronic controller is configured not to permit inflation or deflation of one or more tyres by the system.