A boiler control system includes a room temperature sensor 10 which utilises radio transmission to send temperature information via antenna 11 to receiver 15 via antenna 16. The receiver will provide an output to a control unit 18 to cause actuation of the boiler 19 for example if the room temperature falls below a preset value. The temperature selected can be varied by means of up/down keys 13/14 on the sensor 10. Temperature information can be displayed by means of display 12. Unique coding identifies the transmitting sensor and transmission can be sequenced on a number of frequencies to reduce the risk of reception failure. Additional temperature sensors including a hand held unit each with a unique identity code can be used and transmission time is varied to avoid coincident transmission from the sensors. Telephone linkage for a number of devices can be provided.