The manufacturer of an RV, in this case Heartland, guarantees the unit, generally for one year, and it would be rare that the warranty would exclude diagnostics, parts or replacement labor. The warranty is their responsibility to administer and to fund.
The first source of warranty repairs would be authorized dealers for the brand. In addition, most units use components from vendors ( Norcold in this case) and these vendors cover warranty costs of the manufacturer based on some negotiated formula. Many of these vendors supply to a number of manufacturers and sell on the open market to consumers. Often their individual warranty exceeds that of the overall manufacturer's warranty.
These vendors often have a network of authorized warranty stations and dealers working under a contract. They can often be used in lieu of the RV manufacturers network of dealers. Regardless of the warranty source the manufacturer allows you to use, the terms of the original warranty are not changed.
These networks of warranty stations are for the most part independent businesses that often ignore their contractual obligations. At the end of the day, you should not be responsible for any diagnostic costs unless stipulated in your original manufacturer's warranty. Your source of relief should be back through either the original selling dealer or Heartland. Good luck but they do owe you compensation for your expense.
