Tado extension kit not connecting to boiler

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I have no heating and the boiler is on standby - the extension kit has been reset but the boiler comes on for seconds then goes off. I've asked tado for help but they told me to take a photo of the wiring, that was fine so they told me to reset it and that's it. I can't screw the cover back now but I can click it in and press reset and the same thing happens.