Instant water heaters not generating hot water despite switching it on for a longer time period

Due to poor quality water heaters, citizens forced to use electric kettles
Though the instant water heater which the domain investor purchased had isi mark, from a company based in Gurugram, haryana, it is of poor quality, the water is not heating properly
Initially after the heater is switched on the water is getting heated.
Later the water is not getting heated, despite keeping the heater on for a long time.
It appears that there is a major problem with the thermostat used in the instant water heater
Since the water is not heating, the users are forced to use an electric kettle to heat the water.