Thanks, I've started a return on nest. Where did you get your control from? Was there any additional bits needed?
Vaillant sensoCOMFORT VRC720 Wired Multi-Zone Room Thermostat - Mr Central Heating
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That's wired version, I got wireless one as we are going to have lots of work to do on our house so not sure where final place for it will be. If you want to use their app you will need to get the gateway, we both work from home so no need.
All I needed was a short cable to connect two wires from wireless receiver to boiler ebus terminal.
If going wired you will need more length, not sure if it comes in the package.