My thermostat is at zero and the control box has features for Central Heating and Hot Water . Why can't I separate them??
You furnace is heating your hot water and providing your heat both. When you use hot water, the furnace has to come on to make more hot water. You can't separate them without redoing or modifying the system. At the least you would have to have a tech remove the hot water from the furnace system and then install another source for your hot water and plumb that into your pipes. And that's only if that can be done with your furnace; with some type/models of furnaces you can't separate the two without causing issues. Electric hot water heaters aren't much cheaper to run if at all. You'd be looking at buying a new electric or gas hot water heater, a plumber, a furnace tech, lots of copper pipes and fittings and possibly an electrician to run the wiring. Make sure your hot water pipes and expansion tank for the hot water are insulated. That will help them hold the heat and reduce how much the furnace runs to keep the water hot.
I am guessing that you have a hot water heating system that also heats your domestic water. You may have a water heater that uses hot water from the boiler to flow through a coil type heat exchanger in the tank to then heat the water. There are many types of systems out there and if you are not familiar with yours you should have a tech check it over and explain the system
