A breathing assistance system (1, 100, 200) for delivering a stream of heated, humidified gases to a user for therapeutic purposes, comprising: a humidifier unit (5, 105, 205) that has an inlet port (23, 123, 223) and an exit port (9, 109, 209), said humidifier unit adapted to in use receive a flow of gases from a gases source (13, 113, 213) via said inlet port, said humidifier unit further adapted to hold and heat a volume of water (20, 120, 220) in use, in use said flow of gases passing through said humidifier unit and becoming heated and humidified, said heated humidified gases exiting said humidifier unit via said humidifier unit exit port, a delivery conduit (6, 106, 206) and user interface (7, 107, 207) configured to in use receive said heated humidified gases from said exit port for delivery to said user, said delivery conduit having a heater wire adapted to heat the gases within said conduit, a flow probe (61, 161, 261) adapted to measure the actual flow rate of said gases stream through said system; a patient end temperature sensor (15, 115, 215) adapted to measure the temperature of said gases flow at or close to said patient; and said breathing assistance system further comprising a controller (8, 108, 208) adapted to receive data from said patient end temperature sensor (15, 115, 215) relating to the measured temperature, and data from said flow probe (61, 161, 261) relating to said actual flow rate, said controller (8, 108, 208) determining a control output in response, wherein said control output relates to a target temperature at said patient end temperature sensor for a given flow level, said control output adjusting the power to at least said heater wire to maintain or alter the temperature of said flow of gases within said conduit (6, 106, 206) to match said temperature measured by said patient end temperature sensor (15, 115, 215) with said target temperature to achieve a desired patient end temperature at said user interface (7, 107, 207). a humidifier unit (5, 105, 205) that has an inlet port (23, 123, 223) and an exit port (9, 109, 209), said humidifier unit adapted to in use receive a flow of gases from a gases source (13, 113, 213) via said inlet port, said humidifier unit further adapted to hold and heat a volume of water (20, 120, 220) in use, in use said flow of gases passing through said humidifier unit and becoming heated and humidified, said heated humidified gases exiting said humidifier unit via said humidifier unit exit port, a delivery conduit (6, 106, 206) and user interface (7, 107, 207) configured to in use receive said heated humidified gases from said exit port for delivery to said user, said delivery conduit having a heater wire adapted to heat the gases within said conduit, a flow probe (61, 161, 261) adapted to measure the actual flow rate of said gases stream through said system; a patient end temperature sensor (15, 115, 215) adapted to measure the temperature of said gases flow at or close to said patient; and said breathing assistance system further comprising a controller (8, 108, 208) adapted to receive data from said patient end temperature sensor (15, 115, 215) relating to the measured temperature, and data from said flow probe (61, 161, 261) relating to said actual flow rate, said controller (8, 108, 208) determining a control output in response, wherein said control output relates to a target temperature at said patient end temperature sensor for a given flow level, said control output adjusting the power to at least said heater wire to maintain or alter the temperature of said flow of gases within said conduit (6, 106, 206) to match said temperature measured by said patient end temperature sensor (15, 115, 215) with said target temperature to achieve a desired patient end temperature at said user interface (7, 107, 207).