For? Sink? Toilet? Or whole house?
Need to change out the insides. Need a plumber.
Plumber won't replace the insides. He/she w\ill replace a $5.00 valve and charge $100. This is DIY site.
We need to know on what??? water heater,house,RV If you can get to it easil,turn the water off & reseal or replace
Where is the valve. Most can easily be replaced
Yes, most can be easily replaced. Just be careful, I had a client try to replace one under a bathroom sink, turned it the wrong way, forced it and it cracked the pipe inside wall. The $5 valve ended up costing $4600. in repairs. After that I'm a little gun shy of easy fixes by novices , when it could turn into exspensive repairs to quickly. That is why I recommended a plumber. I'm sure William will post a video for you to follow. Hope you get the $5 fix!