Radiators or heating zones heat unevenly; some remain cold while others are hot.

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

• Bleed radiators: Starting from the highest floor, use a radiator key to release air until water flows steadily. Re‑top system pressure afterward.
• Check valves: Ensure both the thermostatic and lockshield valves on each radiator are open. Adjust lockshields to balance flow.
• Flush or clean system (technician): If some radiators stay cold at the bottom, sludge may be present and a power flush or chemical clean may be needed.
• Adjust pump speed: Set the Sime pump to an appropriate speed or proportional mode if available.