Have moved to an area of very hard water so have had to use the salt compartment in the dishwasher for the first time. I filled it up about 2 weeks ago, and tonight thought I would check how it was doing so tried to open the salt compartment hatch in the floor of the washer. I cant get it open - does it only open when it is empty and need refilling? When I filled it the compartment hatch opened fine, now it only opens a smidgeon.