YES it is the check valve in HOT Out port
Vibrating/buzz noise from failed check valve....O-ring dislodged....plunger cockeyed----reason antifreeze backflowed
RV MFGs install them cause they are cheap and little labor
Standard 1/2" NPT check valve
*If you have room/easy access install a shutoff valve instead of new check valve and just install a nipple
I took my Medication today. HAVE YOU?
Dodge 3500 w/Tractor Motor & NUWA 5vr
US NAVY---USS Decatur DDG-31