Since the valve assembly is partially opening this suggests the operation of the machine is ok and that the problem is the valve assembly. You can take out the assembly and clean the screens and while it is out if you know how to use a jumper cord and a power strip you can hook up water and power to the assembly and see if it opens fully. But don't test it that way unless you are absolutely certain you know what you are doing. Otherwise just try replacing the assembly and that has a good chance of fixing your problem.

Of course the first thing to do is to check and make certain there is no blockage in the inside or external water lines.