Use our N/C normally closed solenoid valve to make it work long hours t would become very hot because there are so many coils inside. It’s normal and safe phenomenon. We continually tests and tracks the product’s working status, the highest working temperature of this product reaches 60℃, and the plastic part withstand extremely high temperatures to 150℃. The rated voltage is DC 12V. It’s safe voltage for people. But this operation is unreasonable. In the product reviews, some buyer also mentioned if someone requires the solenoid valve works for a long time, he should buy N/O normally open solenoid valve, so that it will open all the time without power and will not be hot. Turn on water when system start; and cut off water when system stop. Food Quality and suitable for Reverse Osmosis water system, etc.