p2209 nox sensor heater sensor circuit range/performance (bank 1)

Question

i have a vw golf 1.6 fsi 04 plate. the engine light came on and when i read the fault code with a scan tool it says-p2209 nox sensor heater sensor circuit range/performance (bank 1)so i replaced the heated oxygen sensor and turned the light off.all was fine but 4 days later the light came back on with the same p2209 code.any suggestions on what to look for next would be much appreciated.