Reason：

Thermostat sensor control the heating start and off, if the setting is more than 55℃, it will start again when water temperature reduced 10℃, if the setting is lower than 55℃, it will start again when water temperature reduced 5℃, this can keep water in hot all the time.

Solution：

Water heater is normal, don’t worry.

You may switch off the unit if you don’t need hot water currently, and switch on just before you need it.