Boiler runs but some radiators stay cold

Safety first: Radiators and pipes can become hot; use caution when adjusting valves.

• Check TRVs and valves: Ensure thermostatic radiator valves and lockshields are open on cold radiators.
• Bleed affected radiators: Remove trapped air starting with the coldest radiators.
• Balance the system: Slightly close valves on radiators that heat quickly to encourage flow to colder ones.
• Engineer tasks: Assess pump sizing and condition, flush the system if sludged, and professionally balance the system.