How should I fix the UpdateZoneSizing message? Why does one error produce a warning and the other a severe warning?

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I have the following error messages, but I am not sure why one is a warning and the other a severe warning/error. How can I fix it?

** Warning ** UpdateZoneSizing: Heating supply air temperature (calculated) within 5C of zone temperature
**   ~~~   ** ...check zone thermostat set point and design supply air temperatures
**   ~~~   ** ...zone name = TZ - S6 - AHU 4 VAV
**   ~~~   ** ...design heating load         = 5957.52 W
**   ~~~   ** ...thermostat set point temp   = 25.000 C
**   ~~~   ** ...zone temperature            = 24.993 C
**   ~~~   ** ...supply air temperature      = 27.000 C
**   ~~~   ** ...temperature difference      = 2.00704 C
**   ~~~   ** ...calculated volume flow rate = 2.41854 m3/s
**   ~~~   ** ...calculated mass flow rate   = 2.91094 kg/s
** Severe  ** UpdateZoneSizing: Heating supply air temperature (calculated) within 2C of zone temperature
**   ~~~   ** ...check zone thermostat set point and design supply air temperatures
**   ~~~   ** ...zone name = TZ - S6 - FCU 1
**   ~~~   ** ...design heating load         = 175.39 W
**   ~~~   ** ...thermostat set point temp   = 25.000 C
**   ~~~   ** ...zone temperature            = 25.001 C
**   ~~~   ** ...supply air temperature      = 27.000 C
**   ~~~   ** ...temperature difference      = 1.99877 C
**   ~~~   ** ...calculated volume flow rate = 7.14982E-002 m3/s
**   ~~~   ** ...calculated mass flow rate   = 8.60548E-002 kg/s
** Warning ** Calculated design heating load for zone=TZ - S7 - LIFTS is zero.
**   ~~~   ** Check Sizing:Zone and ZoneControl:Thermostat inputs.

I have since changed some of the values, but I am asking for knowledge and documentation sake. Thank you!