We have a Trane RTU vav model# SFHFC304LK58A4 serial# J96L73488

The issue is the heat works in the unit with no issue in the test mode. When the unit goes into heat on it's own automatically either during morning or daytime warm up. The user interface on the intellipak says Daytime WU 0. The heat never starts heating on it's own automatically. Does anyone know what could cause this to just say Daytime warm up 0? Thanks to all in advanced