Welcome to the Heartland owner forum.
The only place that I can think that the check valve would be is at the water pump.
I don't know exactly how to go about finding out for sure, but I would contact Heartland service or Shur-flow at 1-800-854-3218.
Hi tntoklahoma,
I see I'm a little slow moving tonight,, but Welcome to the Heartland Owners Forum and family. We have a great bunch of people here with lots of information and all willing to share, as Alan has already done.
I am with Alan, don't know for sure, but believe the check is on or near the pump, probably in the discharge line. Pumps do not like to suck through a check valve.
Alan gave you the number to Shur-Flow,,, this is number to Heartland Customer Service, 877-262-8032, someone can get you better information if you need it.
Enjoy the forum and let us know what the problem is.
Jim M