Boiler runs but some radiators remain cold at the top

Safety: Allow radiators to cool slightly before bleeding to avoid scalds.

• Bleed radiators: Use a radiator key to open the bleed valve at the top until water flows steadily, then close. Start with the highest radiators.
• Recheck pressure: After bleeding, top up the system via the filling loop to the correct pressure.
• Check pump speed: If adjustable, set the pump to an appropriate speed to ensure good circulation.
• Investigate air ingress: If air returns frequently, have a technician check for micro-leaks and correct inhibitor levels.