Answer: According to our gcode logic, Before start any FDM printing- our nozzle heat first and then the bed start to heat up. In some case maybe the nozzle is not heating properly and not reaching the initial temp around 200-220 degree, because of this the bed is not heating also. So you need to make sure that the nozzle is heating properly and reaching the initial temp.
If the nozzle is heating properly still the Bed temp is not increasing from the screen then you need to check the bed wire connection from the back of the bed. It still doesn’t work then your heating film needed to replace. Cause maybe it’s no longer heating or not giving signal to the sensor.