Is it just hot water side? If so, did you check the valves on the bypass? If it is all your water. It could be a bad reducer (That you put on the water hose) or regulater you might call it.
I never heard of that second checkvalve before "as mentioned" but it certainly makes sense. See if your has that second check valve.
WOW I learned something new here. Thank You for that info.
Tim-DW(Kathy)
12 Chevy Sonic DD, 03 JEEP GRAND CHEROKEE, 2001 Jayco KIWI
If a "nightmare" is considered a dream-then I am living the dream