ℹ
info Honeywell
Status Aux Heat On
Auxiliary heating system is activated and running.
? What Causes This
Primary heating source cannot meet demand, auxiliary heat is engaged (heat pump systems only).
ⓘ What This Means
This is normal operation for heat pump systems. No action required.
Source: page 7 of the official manual
From the manual
This error code appears in:
Honeywell Th8320U1008 Thermostat