Additionally, if they do call you should be able to troubleshoot over the phone and make the determination on the spot whether it's something that requires a site visit.

Does anyone have any general advice on getting a home rented and trouble shooting this scenario to minimize vacancy?

I really don't know anything about heating cable or how to trouble shoot them.

If they know a HML that requires only 10% of the total cost of project, see if they are willing to front the majority of that 10% for 50% of the profits of the project and basically just be there for trouble shooting while you manage most of the day to day stuff.

At least get someone out to troubleshoot so you can decide if the cost is worth the warranty battle.

The rare thing about it is that if you have any questions you can call and an actual person answers the phone and troubleshoots with you.  

A massive cost that basically requires either a full rewire of the building or potentially extensive troubleshooting.  

Our employees could theoretically see your calculator results, but if I hear of employees doing this for personal gain or without user's permission to solve a troubleshooting problem or fix a bug, I would immediately recommend their termination at BiggerPockets.

The last indicates that you've heard their concerns and are working with the tenant to troubleshoot the problem/situation (Bro Deal). 

If it is an individual breaker, you could troubleshoot it if you are there - but I think you've done the right thing, just have someone look at it.