!!
critical Drayton
Error Code E1
Internal sensor fault — indicates a problem with the internal temperature sensor.
? What Causes This
Fault or failure of the internal sensor within the thermostat.
✓ How to Fix It
Replace the Digistat+2 thermostat if an E1 error code is displayed.
Source: page 2 of the official manual
From the manual
This error code appears in:
Drayton Digistat 2