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

Safety: Allow the 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 the flow is hot but the return is cold, circulation is restricted.
• Bleed radiators: Starting upstairs, bleed each radiator until water flows steadily. Repressurize the system as needed.
• Check TRVs and valves: Ensure all thermostatic radiator valves (TRVs) and lockshield valves are open where heat is required.
• Check motorized 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 motorized valves.
  • Powerflush the system if heavily sludged.

Improving circulation will enhance efficiency and comfort.