The solenoid valve is nothing but a coil of electic wire wrapped around a cyclinder with a soft iron bar magnet in the center. On one end the iron bar is the needle of a needle valve assembly and on the other a spring that holds the needle valve closed when the coil is not powered. There is very little resistence to create heat save that of the natural resistence of the wire in the coil which, under normal circumstances, may feel warm, but certainly not hot, to the touch. If moisture has penetrated the valve such that the bar rusts and cannot properly move (to open the needle valve) it will create resistence in the coil, hence heat, hence time to replace the valve. The solenoid/needle valve is normally before the pressure regulator hence it is wise to have a qualified tech do the work to ensure you get--in this case--less Bang for the Buck.
"It is not so much for its beauty that the sea makes a claim upon men's hearts, as for that subtle something, that quality of air, that emanation from the waves, that so wonderfully renews a weary spirit."