These offer hot water at mains pressure and if installed correctly a balanced hot and cold water supply to all of your outlets. They are a pressurised cylinder and must be installed correctly and have regular servicing. They can also be installed to offer hot water priority, for example if the cylinder requires to be heated it will take priority over the heating. With modern boilers two inputs can be used, one for the hot water to run at its maximum and reheat the cylinder quickly and the second for the central heating to run at a much lower temperature saving money.