Shutting off hot water?

If you have a boiler to heat your domestic water, shutting off the main water supply (cold) will also shut off the supply to the boiler, essentially shutting off the hot water too. You said it has a tank. It is possible to have a domestic water storage tank, but it more likely that the tank is the expansion tank for the heating water loop. That tank will still have boiler pressure even with the supply turned off. That is normally a small tank strapped above the boiler with a drain cock and a single pipe going into the bottom of it. Don't open that drain while the water supply is shut off. The water that circulates to provide space heating is separate from your domestic hot water.