What to check
The door release is triggered by a relay in the power supply, The Red LED should be ON indicating 12v AC is live, the Yellow LED is ON when the relay is energised, test the release by shorting the relay N/O and Com contacts to send 12v AC to the release.
Corrective Action
Replace release
Links
https://www.entryphone.co.uk/shop/productdetail/DL141_M