Tado not calling for heat to supply to radiators

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Hi, I have installed a Tado system to an Alpha boiler (Intec2 28XE)

I don't have any reported errors on the boiler or the Tado system itself, but the radiators are not turning on when trying to get the heating on in the system

This is clear from the display as there should be a radiator icon when radiators are calling for heat

I've attached a photo of the setup. The black cable is connected to CH COM on the Tado wireless receiver and the grey wire is attached to CH NO. I've not made use of any of the purple link cables

Wondered whether anyone had any ideas as to what might be wrong

https://ibb.co/jDBVv2x