Radiators are not heating properly but boiler appears to run

Safety first: Allow radiators to cool before handling valves.

• Bleed radiators: Remove trapped air starting with the highest radiators.
• Check TRVs and valves: Ensure thermostatic radiator valves and lockshields are open where heat is required.
• Clean system filter: If a filter is installed, isolate and clean it to remove sludge.
• Professional balancing and cleaning: A technician should balance the system, check pump settings, and consider powerflushing if sludge is present.