First, muriatic acid it too powerful an agent to use for de-liming coils- try to avoid repeating that. (White vinegar pumped through it for an hour or so with a small pump should do it.)
Tankles coils will crud up both on the boiler side and potable side over time, which limits the rate of heat transfer, even if you have a big enough burner and thermal mass in the boiler that it "should" be able to keep up. De-liming the potable side fixes half the problem, but SFAIK there's no good solution for the boiler-water side. The hotter the water, the faster it will lime up.
If the boiler is in good shape, adding an "indirect" hot water heater that uses boiler water in a much larger heat exchanger inside a hot-water heater tank. If you install it with ball valves in some taps for deliming the heat exchanger on the boiler loop, it should give you good service forever, even if you have to de-lime it every 5 years or so. If you do it that way you can usually set a lower low-limit (or even cold-start) the boiler, reducing standby losses. It can literally double the summer hot-water heating efficiency, and you'll never run out.
They're not cheap, but it's cheaper than divorce lawyers or years of marriage counseling.