1/2" Bronze Combination Fill Valve & Backflow Preventer problem?

[anvilman]

I did some searching, and have identified these parts here in the video, you could see my issue that it’s been leaking. Seems to happen when the heat comes on or for hot water usage. Do I simply replace these two parts in problem fixed? Or is there a problem elsewhere?

 

[Geofd]

Replace that part, disconnect the union on the right side of the union and loosen the fast fill get 2 new nipples the same size