Boiler runs but radiators do not get hot or only partially warm

Safety: Allow system to cool before bleeding radiators. Isolate power before working on valves or pump electrics.

• Check boiler flow/return pipes: Feel the flow and return pipes at the boiler. If flow is hot but return is cold, circulation is restricted.
• Bleed radiators: Starting upstairs, bleed each radiator until water flows steadily. Re-pressurise the system as needed.
• Check TRVs and valves: Ensure all thermostatic radiator valves (TRVs) and lockshield valves are open where heat is required.
• Check motorised valve: For systems with external 2-port or 3-port valves, feel if the valve body gets warm and listen for movement when heating is called.
• Engineer tasks:
  • Test and replace a faulty circulation pump.
  • Free or replace stuck motorised valves.
  • Powerflush the system if heavily sludged.

Improving circulation will enhance efficiency and comfort.