A domestic heating system 20 serving a space-heating circuit 2 and a domestic hot waster circuit 4 has: a base unit 21 which is located next to boiler 7 and which monitors and controls operations of the system 20; a room unit 22 located in a room containing radiator 3 of the space-heating circuit 2; a mid-position valve 23; a cylinder sensor 24 and a frost kit 25. Base unit 21 has a microprocessor-run communications and control function to process appropriate information from the elements of system 20 and to ensure suitable operation of those elements at all times.