It’s going to cost me £600 to have a Hive combined heating and hot water system installed in my 4yr old Grant oil combi boiler. How does the system operate on the hot water? Is it just a timed control stopping the water flowing through a heat exchanger or is it temperature controlled just by the main boiler stat. Most importantly would it be cost effective? If you can share a little wisdom on this it would be much appreciated. Thank you.