!!
critical Honeywell
Error Code Display blank
Thermostat display shows nothing, indicating thermostat and heating/cooling system have stopped working.
? What Causes This
Batteries are completely dead or incorrectly installed.
✓ How to Fix It
- Remove batteries.
- Insert backward for at least five seconds to reset thermostat.
- Replace batteries correctly with fresh AA alkaline batteries.
- If display still does not come on, gently clean battery contacts using a soft pencil eraser.
- Reprogram the thermostat (see pages 14-15).
Source: page 9 of the official manual
From the manual
