Q: Heater blows hot for 10 minutes, then it blows cold.

Hello, thanks for writing in. This problem could be either an engine thermostat that is not keeping the engine at a constant running temperature (temp gauge steady in the center), or the heater control valve or controls are malfunctioning not allowing engine coolant into the heater core (passenger compartment). It is also possible that the heater controls are allowing cold outside air to "blend" with heated air by not closing one of the ducts in the HVAC unit. I would recommend having a heater inspection completed by a mobile, professional mechanic, such as one from YourMechanic, who will come to your location, diagnose this problem, give you an accurate assessment of damage and cost estimate for repairs.