How do you release a stuck proportioning valve?

To release a stuck proportioning valve, begin by inspecting the valve for any visible signs of corrosion or debris that may be causing it to stick. Apply a penetrating lubricant to the valve's moving parts and allow it to soak for a while. Gently tap the valve with a rubber mallet to help break any corrosion bond. If it remains stuck, consider removing the valve for a more thorough cleaning or replacement.