Hello ,My 15 year old HVAC went down today, the motor needs to be replaced it will cost me over $400 and the refrigerant needs to be added that costs another $300 , just the diagnosis costed me over $250.

It costs more to reinstall and add refrigerant after installation.

So the tenant in my rental was complaining that the refrigerator panel where the water and ice come out would pop off occasionally, but mentioned that it wasn't a big deal because she doesn't use the water or ice.

Refrigerator parts are damaged.

Filters, refrigerator filters, batteries for smoke detectors and fan remotes, light bulbs, etc.Your list is pretty thorough though, I'd only add to make sure you're doing a semi-annual HVAC maintenance.

Regarding appliances, I had to personally drive 5 hours to get the refrigerator my wife wanted, and our range only made it thank to my wife's social media presence and one of her followers from across the country helping us by ordering it (it was only available for local delivery) and repackaging it for Fedex freight across the US.  

Apparently his refrigerator failed, and he went and bought a new one.

For example, warranty repair on a refrigerator probably pays half what an appliance tech typically charges, so they're losing money working on your warranty item.

@Dax Squillante  Using your numbers (which I would be very surprised if you can keep your costs that low), your breaking even with zero cap ex reserves (one piece of equipment needing to be replaced like an AC system, furnace, refrigerator, etc, would put you at a loss for quite a while).  

I've rented a small storage facility and are keeping an extra refrigerator and range in there for those type of situations.