The reasons why the solar water heater controller beeps when plugged in and the light does not come on are as follows:

First of all, check whether there is poor contact between the power socket and the plug. This fault is usually caused by of.

If the contact is poor, use a multimeter to measure the resistance between the L live wire and the N neutral wire of the power cord plug. If the meter needle swings, it is generally normal. If it does not swing, open the water tank side cover and check the power cord. And whether there is poor contact in each connector.

And measure whether the power cord connector and power cord plug in the side cover are connected, and whether the temperature switch and electric heating tube are normal. Check and troubleshoot in order.