Carrier Digial Thermostat registers wrong Temp

2 years ago we had a brand new high efficiency furnace / AC unit installed. Just recently we noticed that the digital thermostat was registering the incorrect temp. It is stating the house is about 5 degrees warmer than the actual temp. Desides just offsetting the thermostat for the temp - does anyone have any ideas on how to fix this issue? Please post to the group.
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