Enable the recirc in the option menu (Opt) on the Touchscreen.
You can discard this alarm performing a long push on the central button.
NOTICE: Bad settings for recirculation leads to big energy consumption.
A permanent recirculation (H24) at 0.5gpm usually drags an average 800W meaning almost 7200kWh used per year only for this.
Financially speaking, that's a 1000$ bill at the end of the year (at 0.14$/kWh).