As with every story, there is a 2nd side. The check in instructions were not updated with the new code, that was my mistake. I take full responsibility. He called me and I answered right away to provide up to date details. the website was also updated.
The problem was solved immediately. The WiFi needs to be reset sometimes. This is something I have experienced in many places with many different providers. Once reported, the WiFi was reset right away, as well. As for the door and lock, there literally is nothing wrong with those items. The door needs to be shut tight to latch and that is all. I believe there was difficulty in understanding how those items work even after explanation and I believe this was mainly due to frustration on the guests part. I understand the frustration really began after the hot water was found to be inoperable. This particular water heater is a hybrid and more complicated than a typical water heater. Although a repair was made and hot water was verified to be in working order prior to check in, an additional part went bad within the next few days, prior to check in. Due to the time required to order the warranty part, I offered the guest to check out with a discount for the first night and a full refund for the two nights remaining. He seemed hesitant so I also offered him to stay with a discount and he could shower in a vacant home, three doors down. Additionally, the plumber completed a bypass which provided warm water (understandably still not ideal as it wasn't hot). He chose to stay and I was surprised when a full refund for the additional nights was still requested afterwards. At that point, I felt as though he was taking advantage of the situation. As any home owner is aware, sometimes things happen and can't be anticipated regardless of the price spent to provide high quality appliances. With that being said, I felt I did everything in my power to address his concerns even though I was on vacation myself.