Furnace runs but the house is not heating adequately; radiators or ducts are lukewarm.

Safety: Turn off power before opening panels; be cautious of hot water and surfaces.

Steps:

• Check setpoints: On the Buderus control (e.g., Logamatic), verify that the heating curve and maximum flow temperature are set appropriately for your climate and emitters.
• Bleed radiators: Use radiator bleed valves to remove trapped air until water flows steadily. Refill the system to proper pressure afterward.
• Inspect circulation pump: Confirm the Buderus pump is running and not set to an excessively low speed. Many pumps have adjustable speed settings.
• Check mixing valve: If a 3-way or 4-way mixing valve is installed, ensure it is not stuck in a low-temperature position. Manually exercise the valve if possible.

If performance remains poor, a technician should perform a full hydraulic and combustion check.