Indoor unit runs but no cooling, air feels only slightly cooler than room temperature

Safety: Do not attempt to handle refrigerant without proper certification. Running the unit with low charge can damage the compressor.

• Check basic airflow: Ensure filters are clean and fans are running normally.
• Feel the pipes: With the unit in COOL mode, carefully touch the insulated suction pipe at the indoor unit. It should be cold and may sweat. If it is only mildly cool or warm, charge may be low.
• Inspect for oil stains: Look at all flare connections and coils for oily residue, which indicates a leak.
• Stop prolonged operation: If cooling is very weak and you suspect low refrigerant, avoid running the system continuously to protect the compressor.
• Call a Vaillant technician: A certified technician should perform leak detection, repair leaks, evacuate, and recharge the system to the exact Vaillant‑specified charge.