can someone tell me what the difference is between a wall hung tankless water heater and a wall hung boiler? and when would one use one vs the other?
A tankless system is designed for producing potable hot water instead of a conventional water heater. A boiler is designed to provide heat to a dwelling. A side benefit is the ability to heat a tank of water using a zone and an indirect water heater tank.
A tankless system, because it is heating water as it passes through and then dumped down the drain, won't get the water hot enough for many space heating purposes. A boiler, because it can recirculate the water is able to produce much hotter water, typically required for radiators.
Important note - I'm not a pro
Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013