The Leanest Maintenance is no maintenance. Root Cause Analysis (RCA) eliminates whole maintenance situations by eliminating the causes of those situations. Nothing is more lean than no problem in the first place.

Toward the end of the heating season one year, I received a call to say there was no heat in a single-family rental house I owned. I visited the house, examined the forced-air furnace, and found the heat exchanger was shot. I hired a local handyman to replace the unit. I did not receive another complaint so I forgot about the issue.

During the first cold snap the next winter I got a call from the family, again complaining about lack of heat. This time I sent a licensed HVAC contractor to look at the heater and repair it if necessary. He reported that the transformer was bad, and he had replaced it, and sent a bill for the service call. I didn't get another call from the family, so I assumed the problem was solved (the weather warmed up also). A week or two later I got another heat call. I asked the same contractor to take a look. Another technician looked the heater over and found the transformer had failed and now the thermostat also was not working.

Now I was annoyed and asked for some consideration since I thought the contractor must have used a bad transformer, which I didn't want to pay for twice. When the third complaint came in I called the contractor...