Radiators only partially heat up or some remain cold while boiler runs

Safety: Radiators can be hot; use gloves when touching valves.

User checks:

• Bleed radiators: Remove air from all radiators, especially those that are cold at the top.
• Valve positions: Ensure both flow and return valves on each radiator are open. Thermostatic radiator valves should not be stuck closed.
• Filter (if accessible): If a magnetic filter is installed externally, follow manufacturer instructions to clean it (if user-serviceable).

Technician actions:

• Balance the heating system by adjusting lockshield valves.
• Flush radiators and the Fondital hydraulic group to remove sludge.
• Clean or replace the system filter.
• Check and adjust pump speed or replace the pump if underperforming.