[Larry]

I would like to add that you need to be sure that the circulating pump is not dead headed for an extended period of time. If the domestic water heating is the only loop on that pump it could damage it. To avoid this you can use a 2 position valve that provides a return path for the coolant when heat is not called for and a path through the heat exchanger when heati s called for. Perhaps this is what Jon has or there is more on that loop. It was not apparent from his post.

[Harry]

I do not have a sole loop to the HW tank.