Is it ok to shut off the main water supply into the house while on vacation and leave the heat on? Have an oil fired forced hot water system with a hot water tank that is heated by hot water from the furnace(has hot and cold inlets/outlets on top and heat water inlets/outlets on side). In other words does there have to be pressure available to the heating system at all times?
keep water to the boiler all the time --
you could have valving & piping installed such that the rest of the inside plumbing would be without pressure.
I leave on my outside frost- free faucet, but the rest of the house inside has no pressure. so neighbor could water plants, fight a fire --