Trane XE90 Furnace Fan Always On

[Espritman]

We have 2 XE90 propane units in the house. Although the thermostat is set on 'Off' vs. 'Heat' or 'Cool' and fan is on 'Auto', the fan runs constantly and the vent pipe from the furnace to the outside is also blowing air. The sight glass on the furnace shows a red light blinking 5 times every few seconds. I've searched online for a manual but it seems impossible to retrieve. Thank you.

 

[user 4883]

Which fan are you talking about the circulation blower motor or the combustion blower motor?
Vent pipe to the outside would be the combustion blower and the fan related to the T-stat ON versus AUTO setting would be the circulation blower motor.