S-plan system: hot water LED on when only heating required?

I've got a tado system with wireless receiver. My heating system is an S-plan. When I program tado to only make hot water for the hot water tank, the right valve opens and the valve for the heating system stays shut. However, when I program tado to only deliver heat and no hot water, both valves are open + both LEDs. If I had somehow wired the system incorrectly, I can see how both valves might open up even though I only call for heat., but the LEDs are both lit, so although I'm not requesting hot water, the wireless receiver is nevertheless calling for it when I only call for heat.

Any suggestions as to what might be wrong?