Hot Water Circulator:

Central heating system consists of all the pipe work and radiators that are connected to the boiler. The boiler provides the heat but, it's the pump (Circulator) that moves the heated water from the boiler through the pipe work to the radiators, and back to the boiler for re-heating.
There are many types of system that can be installed, and which may be tailored to your own preferences. But a carefully designed and installed system will give many years of trouble free running and will not waste heat, therefore keeping fuel costs low
Your E & E engineer will be able to help and advise you choose the best system for your home
Independent Water and Heating:
This means the heating of the water and the heating of the radiators are done by different boilers, so for example a water heater would supply the hot water and a central heating boiler would supply the radiators.
In a lot of cases the water heater is fitted first to get cheaper hot water than from an electric immersion heater. The only problem with this system is that it takes up two lots of wall space.