The Honeywell VisionPro IAQ Thermostat consists of a 3-wire thermostat and an Equipment Interface Module (EIM).
Errors from the thermostat or system (X/L Terminal) will display an error code and a red light on the thermostat.
Error Codes:
| Error Code | Condition |
| 027 | Faulty thermostat (must be replaced) |
| 035 | Duplicate thermostat zone detected |
| 036 | Duplicate UV timer |
| 037 | Duplicate filter timer |
| 038 | Duplicate humidifier pad timer |
| 039 | Duplicate indoor humidity sensor |
| 040 | 24V detected on X/L terminal |
| 050 | Duplicate outdoor temp sensor |
| 052 | Faulty post-coil air sensor |
| 053 | Faulty outdoor temp sensor |
| 054 | Faulty indoor humidity sensor |
| 089 | Heat/Cool equipment is missing |
| 090 | Data interface is continuously busy |
| 091 | Thermostat is not receiving data |
| 118 | Faulty discharge air sensor |
| 119 | Faulty temperature sensor |
| 121 | Duplicate post-coil air sensor |