Heater not working when in idle

Hello, could there be an air pocket in the cooling system -- but that would mean that some kind of repair may have been performed in the past. Other than that, it could be that the thermostat is opening way too soon or sticking open, not allowing the engine to get to the proper operating temperature. Any way you look at it, hands on testing is required to figure out what is going on. www.repairpal.com/repair-shops