Getting fluctuations in temperature during npt run

GROMACS version:2021.2
GROMACS modification: Yes/No
Dear users,
I am simulating a polymer using gromos forcefield parameters. After minimization, i ran canonical ensemble (NVT). During NVT i got a temperature fluctuation of ± 5K about its average value which is 425 K. Now when I switch to the NPT ensemble, my temperature fluctioans are increasing. During NPT temperature is fluctuating ±50 K about its average value which is 425. I did ibserve the system for 2ns.
Please help me to minimize the temperature fluctuations of my system.

What thermostat settings did you use in each phase of the simulations? Methods like V-rescale have intrinsically much smaller fluctuations than, e.g. Nosé-Hoover, and you can modulate the magnitude of fluctuations with τT for both.

Thank you for your reply. I have changed the thermostat from Nose-Hoover to V-rescale and it worked. Now the temperature fluctuation is less.