Taco Discharge Valve not closing all the way

I’ve had this pump and dump heat pump for 12 years. About a year ago the discharge valve stopped closing all the way. I could hear a noise and it was the water still running through the valve because it was about 95% closed. So I would manually close it the rest of the way. I was told that the zone valve was not the right one for the discharge.....it didn’t have enough shutoff pressure. It worked perfect for 10 years and now it just burnt out and quit working completely. I replaced the head with a new Taco ZA024Q4A1. It works perfect again but my guess is it will be temporary. There is iron in our water so I’m sure the valve itself is caked with iron on the inside. Is there a way to clean the actual valve that the water runs through somehow?