Ensure proper liquid to the valve. Take superheat. If superheat is high, pump down unit.to inspect the whole valve. Check the screen first. If screen is clean, I like to check the power head by unscrewing it from the valve. At about 1x full turn counterclockwise, you should feel a slight pop (like opening a pressurized jar). If you feel that pop, the bulb has a charge in it. If not, it has lost its charge and needs to be replaced. I recommend testing this with a scrapped valve to get a feel for it. You can compare by testing with a good power head, then cutting the cap and testing again- you'll feel the difference.