The hotel's solar water heater, why does the hot water suddenly get hot when taking a bath? What should I do?

The hotel's solar water heater, when taking a bath, the hot water in the solar water heater is mixed with tap water and cold water to form bath water with appropriate temperature. The hot water suddenly became hot. There must be no or too little cold water in the tap water. Check whether the tap water pipe is unblocked. Is it reasonable to use water for water pipes? If you are taking a bath, you should flush the toilet. As soon as the toilet water is discharged, the water pressure in the pipeline will be low, and the supply of cold water will be small, so it is natural to change to hot water. I want to install a cold water tank or stabilize the water pressure in the tap water pipe.