The fill valve you need is dependant upon the capacity of the unit you are working on. Take a look at the model number. It will look something like NHMC-010. That is a 10 pound per hour model. The fill valves are rated by pounds per hour. Below is a list of all the fill valves made for the the electrode and electric heater style units. If you are still not sure about which part number you need, find your model in the left hand link bar and click on it. Once on the parts page for your model you will find a link to an owners manual. In that manual you will find a complete parts list which will tell you the correct part number. You can also contact us and we will tell you what the part number is.