Boiler runs but some radiators stay cold or only warm at the bottom

Safety: Radiators and pipes can be hot; use caution when touching.

• Bleed affected radiators: Use a radiator key to release trapped air until water flows steadily.
• Check valves: Ensure both TRV and lockshield valves are open on cold radiators.
• Balance system: Slightly close lockshield valves on radiators that heat quickly to encourage flow to colder ones.
• Engineer actions:
  • Powerflush the system to remove sludge.
  • Add inhibitor to protect against future corrosion.
  • Check pump sizing and performance relative to the system.