Good morning Michelle, my name is ***** ***** I will assist with your query today.
Firstly the thermostat has lost its memory, so it will need 'paired' to the receiver on your boiler, so you are correct in suggesting you need to press the button marked 'do not use'.
The process for pairing your thermostat with the boiler is detailed in the manual here, on page 4.
You need to press the "learn" \ "do not use" button on both the thermostat (found on the back), and also the receiver in the boiler (found at the front).
Please let me know if you need any further assistance.
Excellent, appreciate if you rate the service received.