1. Heater Matrix (Heater Core) Blockage: While less likely if the pipes are hot, the heater core itself could be partially or completely blocked. This prevents hot coolant from transferring its heat effectively. This is a more involved fix, requiring potential dashboard disassembly.
2. Heater Control Valve Problems: The valve controls the flow of coolant to the heater core. It might be:
* Stuck closed: No coolant flows to the heater core, despite the engine getting hot.
* Stuck open (less likely in this scenario): This *would* result in hot coolant reaching the core, but you should still feel some warm air unless there's another issue.
* Faulty: The valve itself could be electrically or mechanically failing, preventing proper operation. This requires testing the valve (using a multimeter, or simple visual inspection - make sure its cable isn't snagged) and potentially replacement.
3. Blower Motor Problems: The fan that blows air through the heater core might be:
* Not working: This is a common issue. Check the fuse first (consult your owner's manual). Then, try tapping on the blower motor (carefully!) to see if it starts working. If not, it likely needs replacement. This usually involves accessing it beneath the dashboard.
* Low speed only: The motor might be weak, only working on low speed.
* Faulty resistor pack (speed control): This controls the fan speed. A faulty resistor can cause the fan to only work on one speed or not at all.
4. Airflow Blockages: Something might be blocking the airflow path:
* Blocked air vents: Check all interior vents to ensure nothing is obstructing them.
* Vacuum leaks: The vacuum system controls the air flap directing air to the heater core or other vents. Leaks can disrupt this system.
* Dust and debris in the heater system: Over time, dust and debris can accumulate, restricting airflow. This would require more intensive cleaning.
5. Blend Door Problems (Air Direction): This mechanism controls the mix of hot and cold air. If it's malfunctioning, it might be directing all air away from the heater core.
Troubleshooting Steps:
1. Check the fuses: Look for blown fuses related to the blower motor and heater.
2. Test the blower motor: Turn the fan to its highest speed. If it doesn't work, or only works on one speed, the motor or resistor pack is likely at fault.
3. Check the heater control valve: Locate the valve (usually near the heater core hoses). If it's easily accessible, try manually operating it (if possible) to see if it moves freely.
4. Inspect the air vents: Make sure all vents are clear of obstructions.
5. Feel the heater hoses: If one hose is significantly cooler than the other, it suggests a problem with the heater valve or a blockage in the heater core.
6. Listen for any unusual noises: Unusual noises from the blower motor can indicate a problem.
If you're not comfortable working on your car's heating system, take it to a qualified mechanic. Diagnosing this issue accurately often requires some experience and specialized tools. The dashboard needs to be partly or fully removed to access most of the heating system components in a Mk3 Golf.
