The Leak Sealer F4 is an internal leak sealer designed to seal small, inaccessible leaks and weeps that may cause pressure loss and boiler failure. Once dispersed within the system, the product finds the area of oxygen ingress and forms a polymer to seal the pinhole. The unique sealant efficiency of this market-leading water treatment chemical prevents blockages or restrictions within the boiler or vulnerable system components such as pumps and safety devices within 1-24 hours after application. It is possible to seal a leak quickly and efficiently without having to drain the entire system. The Fernox Express range uses Barrier Pressure Pack technology and compressed air propellent to expel the product so the entire range is non-flammable. The propellent (compressed air) is not mixed with the active product so there is no risk of air ingress into the system which could accelerate future risk of corrosion.