Radiators are only warm at the top or some radiators stay cold while others heat up.

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

• Bleed radiators: Use a radiator key to bleed air from all radiators, starting from the lowest floor. Catch water in a cloth or container.
• Re-pressurise system: After bleeding, top up the boiler via the Thermona filling loop to the correct pressure.
• Check TRVs and valves: Ensure thermostatic radiator valves and lockshield valves are open on cold radiators.
• Adjust pump speed: Increase the pump speed setting if the system is large or has long pipe runs.
• System cleaning (engineer level): If radiators remain cold or partially warm, a power flush or chemical clean may be required to remove sludge.