My plumbing is set up to isolate my domestic water from the heating system so I can turn off my domestic hot and cold water (sinks, showers, toilets, etc) but still have water going to my hydronic heating systems... one zone is in-slab radiant heat and the other zone is hot water baseboard.
When I'm away for the winter I turn off the domestic water but leave the heating on.
Guess I'll have to find out if that's the case for my house too! Thanks for the tip.