I have nothing that looks anything like that. I have a square thing with a black screen which came with a tiny manual calling it a Programmer and the square grey thermostat
You're correct in what you're saying and there does have to be a receiver somewhere for that thermostat as they cant talk directly to the timer. Possibly in the airing cupboard or wherever the zone valves are. If they lose connection they can be a A'hole to reconnect.
If it doesnt light up at all after turning the fused spur off and on, the receiver is dead. If you press the bottom grey button, it should bring the heating on manually. The receiver will need replacing but they are only available from BG
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