This is a M picture but the H is the same operation. Provided everything is free and no blockage from cylinder to liftall one of the two pins push to releases fluid back to the reservoir from the left rear port. Other pin releases the other ports. Make sure lever on side of center housing is moving forward completely. Simple to check for external problem. Put a bucket under the left rear outlet and loosen hose enough to drip. If it starts dropping the problems internal. No drop it's external. If the front drops the operating linkage is moving enough to push the first pin in.