Boiler runs but radiators are only warm at the top and cold at the bottom

Safety: Radiators may be hot; allow to cool before removing any components.

• Bleed radiators: First, bleed air from radiators. If they remain cold at the bottom, sludge is likely.
• Individual radiator flush: Turn off both valves on a problem radiator, remove it, and flush it outside with a hose until water runs clear.
• Add inhibitor: After refilling, add a quality central heating inhibitor via a radiator or dosing point to slow further corrosion.
• Power flush: For widespread sludge, a professional power flush of the entire system is recommended.