Leaks in water systems can result from external frost damage, dry solder joints, accidental perforation during maintenance or decoration, or internal corrosion. Sealing internal leaks (central heating systems only) Small leaks, including pressure drops on combination boilers and other sealed systems, can be repaired using Fernox Leak Sealer F4. Each Leak Sealer F4 product treats 100 litres or up to 10 single radiators. On an open vented system, pour the Leak Sealer F4 into the tank and simply draw off 5-10 litres of water from the drain cock initially returning this to the header tank to ensure that no treated water is thrown away. Repeat the previous step until all Leak Sealer F4 has been absorbed into the circulating system. Switch on the circulating pump and apply at least a small amount of heat to achieve even distribution. An alternative solution for dosing is to inject Fernox Leak Sealer F4 Express or Fernox Superconcentrate Leak Sealer F4 directly into the radiator via the bleed valve. Repairing external leaks (to all types of water pipes) To repair leaking external pipes and fittings, use Fernox LS-X External Leak Sealer with a bandage of PTFE tape or another suitable reinforcement tape. After turning off the water and draining down to remove water pressure from the leak, apply Fernox LS-X External Leak Sealer to a dry surface around the area of leakage. Wrap the pipe with a layer of PTFE tape or other reinforcement tape with 50% overlap and extend well beyond the area of the leak. Immediately apply repeat coats of Fernox LS-X External Leak Sealer and further layers of bandage to form a repair about 5mm in total thickness before allowing to cure.