temperature stays low.

hi dear users . i am simulating water flow in a nanochannel with copper walls with lammps I have 1058 water molecules in a cubic nanochannel with 31.66 angstrome height,i want to simulate in 300K degree , but when i fix copper and water on 300K (fix all nvt 300) it fainaly stay on 219K and doesnot raise anymore , when i fix on about 430K it stayes on favorite temperature(300K)! or for example if I fix nvt 1000 , then the system stayes on 750K degree! Why this happens?please help if every body knows its reason . thank you dear users .

How are you printing out the temperature
of the water? Have you printed
the temp of water and Cu separately?