Boiler runs but some radiators are hot and others remain cold, even after bleeding.

Safety first: Allow radiators to cool before adjusting valves.

• Check TRVs and lockshields: Ensure TRVs are open and not stuck. Slightly close the lockshield valves on the hottest radiators to push more flow to colder ones.
• Bleed cold radiators again: Air can collect in upper floors; bleed until water flows steadily.
• Engineer tasks: A heating engineer can powerflush the system, remove and flush individual radiators, and professionally balance the system.