If you have any of these - they are all based upon an aged 868 MHz RF protocol called RAMSES-II.
Your heat source (a boiler?) is probably controlled by a Honeywell BDR91A, or a HC60NG (R6660D) wireless relay module.
HA just now has support for these via this custom component: https://community.home-assistant.io/t/honeywell-ch-dhw-via-rf-hgi80-hgs80-includes-evohome
You will need to invest in a USB RF dongle - approx £25.