For hot water production, you might find the best temperature is 190-170 or so. Maybe 200-180. When there is no tank, the water gets heated by flowing past the hot water in the boiler's tank reservoir. You get decent heat transfer only when there is a big temperature difference between them. The water flows by it for only a short time and distance, so if it isn't hot enough, it doesn't get hot. Think passing your hand through a candle flame. Do it fast and you might not even notice it's warm. Try the same thing with a blowtorch, though, and you'd notice the difference.
Older boilers don't like the cooler temperatures...you could get more condensation in the chimney, too, which could lead to other problems.