I was told not to do what you are doing since it isnt very good for the internals in the water jacket and the gaskets. I too went with an indirect Crown Megastor. My tankless coil was not delivering enough hot water due to hard town water. I didnt abandon the tankless, simply used the output to supply the crown and had a seperate zone with seperate pump to heat the DHW. I turned down the aquastat in the tankless by 40 degrees and lowered the stat on the Crown. I would guess the boiler would fire once a day or so to heat the water in the Crown and that is about it. The crown is stainless and has lifetime warranty so I wont have to worry about it. Operating the boiler to heat the DHW keeps the internal temps hi enough inside the furnace where I dont get any leaks and dont have to worry about condensation inside the boiler. I also insulates all my pipes. I am guessing I cut the standby use by half with most going to make the DHW. If I were to do it over, I would have bought a cold start type boiler where it isnt bothered by this and wouldnt have to be operated in the off season.