Leak Sealer F4 is an internal leak sealer developed for use in a central heating system to seal small, inaccessible leaks and weeps which may cause pressure loss and boiler breakdown. Once dispersed within the system, the product finds the area of oxygen ingress and forms a polymer to seal the pinhole. Effective in 1-24 hours after application, the unique sealing efficiency of this market-leading water treatment chemical has been proven to not cause blockages or restrictions within the boiler or vulnerable system components such as pumps and safety devices. A leak can be quickly and efficiently sealed, without the need for a complete system drain down.