Boiler runs but radiators do not get hot or only partially heat up

Safety: Allow the system to cool before bleeding radiators or opening valves.

• Check radiator valves: Ensure both flow and return valves on each radiator are open. Thermostatic radiator valves should be set above minimum.
• Bleed radiators: Use a radiator key to release trapped air from the top of each radiator until water appears. Re-pressurise the system as needed.
• Check pump speed: Some pumps have adjustable speed settings. Ensure the pump is set appropriately for the system size.
• Clean system filter: If a magnetic filter is installed, isolate it, remove the magnet, and clean out sludge.
• Professional powerflush: If circulation remains poor, a heating engineer may need to powerflush the system and clean or replace blocked heat exchangers.