R - B 2
Solving Err 91 Comm Errors
Err 91 displayed at the Comfort Control
When Err 91 is displayed at the Comfort Control,
thermostat will go to OFF
At the gas furnace (See Figure 1) or air handler (See
Figure 2) is the COM LED flashing slowly in groups
of 2, 3, 4, or 5 flashes indicating number of devices,
OR is it flashing fast?
Figure 1
If the COM LED is flashing slowly in groups of 2,
3, 4, or 5, see Troubleshooting Chart ERR 91 dis-
played at the Comfort Control.
If the COM LED is flashing fast, see System com-
munication troubleshooting (Page 10).
Figure 2
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