Elson Coral E water overflow

[Sergejs]

Hi,

I have an issue with my Elson Coral E water heater. My expansion tank constantly overflows and the water is constantly leaking into the drain. I have checked and the float valve is not the cause of problem - no water running from there.

I suspect that an element inside that controls the water pressure from the main does not work properly. Could you please tell me what potential issue could be? Could it be damaged heating coil that let water run instead of stopping it once the tank is full?

Thanks

Sergej