I have a trane xb80 that is about 8 years old and the fan runs all the time can anybody help with this problem?

If the blower is on all the time with no heat, the system has faulted out for some reason-- Open limit, burners did not light, pressure switch did not close the list goes on. You should have a light blinking on the control board gining you the code to what has failed. You can reset the control by turning the power off going to the furnace and then back on. If the system is heating but the blower never shuts off. Check your thermostat make sure the fan switch is in auto.