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Ideal boiler not responding to call for heat/hot water

I've had an extension kit fitted today to an Ideal Logic Max Heat via OpenTherm. When I call for any heat/HW, the boiler does not respond, and only shows the standby '00' code, and no error message.

All devices are paired, and firmware updated (81.1 on extension kit, 54.20 on thermostat). Thermostat is set up for OpenTherm as per the installation instructions (TS - HC01 - HW - Ek - D01).

Any ideas why the boiler is not responding?