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

Safety: Allow radiators to cool slightly before bleeding to avoid scalds.

• Bleed radiators: Starting with the highest floor, bleed each radiator until water flows steadily. Re-pressurise the system as needed.
• Check TRVs and lockshields: Ensure thermostatic radiator valves and lockshield valves are open enough to allow flow.
• Balance system (qualified person): Adjust lockshield valves to balance flow so that all radiators heat evenly.
• Clean system: If some radiators remain cold at the bottom, a powerflush and installation of an Alpha magnetic filter may be required.