Heating water through a coil is seems like a heck of a waste during the non heating season and many times people complain about running out of water or water excessively hot.

Personally I like gas fired water heaters especially the rapid recovery type.

Water heaters are simple in design and have only one safety (T&P) and one operating controller a boiler has several safety devices and for the most part cannot make water fast enough for peek demand periods as it does not have the volume unless oyu add a tank like hot water maker that is treated as a seperate zone and has a coil inside that heats the water inside the tank so you have volume to play with