Some Laser 73 heater have seen 25 or more years of service. Since the unit is kind of modular, they are easy to repair. Over time the unit would get a new burner, blower motor and maybe even a new heat exchanger while being serviced. While the parts that get heated and cooled all the time are the first to go, the electrical components can last for a long time.

I just serviced a unit that is over 25 years old. It has had a number of the parts changed over time. One thing that has never been changed was the fuel pump. As long as it provided the correct fuel flow, it was good to go. This service showed a fuel leak around the sump area. I miss diagnosed the leak the first time. Because the top of the sump showed fuel after running a short while, I thought the float and valve were the cause. Without a good look at the sump, I changed it out with a new one. This did not solve the problem. Further looking showed the fuel was coming from the pump itself. The O rings on the inside of the pump were leaking. A new pump and controller solved the issue. This was a first for me.

Be aware if you have older units. They are easy to fix. It's just sometimes you have to go pretty deep.