Furnace runs, but radiators or underfloor heating remain lukewarm or cold.

Safety: Allow the system to cool before bleeding radiators. Use a cloth to catch water.

• Bleed radiators and manifolds: Starting from the lowest floor, bleed each radiator or underfloor manifold to remove trapped air. Top up the system pressure as needed.
• Open valves fully: Ensure all radiator valves and any zone valves are fully open while troubleshooting.
• Clean filters: Locate and clean the heating system filter or strainer near the Nibe unit.
• Adjust heating curve: In the Nibe menu, increase the heating curve slope slightly and observe if room temperatures improve over several hours. Do not make large changes at once.

If comfort is still poor, a heating engineer should check the system design and balancing.