Follow instructions in your owner’s manual to disassemble the pump assembly. Check the plunger cup to make sure it is correctly attached. Add a little petroleum jelly. Inspect the check valve at the bottom of the cylinder to make sure it is on and is not obstructed by dirt. Reassemble. If problems persist, plunger cup or check valve may need replacing. Check your retailer or call 1-800-9-SPRAYER for a parts kit.