Leak Sealer F4 500ml

Product Code:

56603

Leak Sealer F4 is a internal leak sealer developed for use throughout 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 within 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.

Ideal for reducing pressure loss from sealed systems
Seeks out and seals inaccessible, internal microscopic leaks fast
Saves time and money on draining down the system and repair costs
Safe to use – does not cause blockages in pipework or vulnerable boiler components such as pumps, air vents and heat exchangers
Designed to be left permanently in the system – compatible with all metals and materials, including aluminium
One 500ml recyclable bottle treats up to 130 litres of system water (16 radiators) and the equivalent of 250m2 of underfloor systems.

Application

The recommended ‘in use’ concentration of the product is 0.385%. One single dose of this product treats a larger sized property with a heating system of 130 litres, up to 16 radiators or 250 sqm of underfloor heating. For open vented systems add via the feed and expansion tank. For sealed systems add via a suitable dosing point (e.g. a towel rail or an in-line system filter). Alternatively, use a suitable dosing vessel to inject the product into the system. In single feed indirect cylinders, e.g. ‘Primatic’ or similar, potable water chemicals must be used.

Physical Properties

Fernox Leak Sealer F4 is a polymer emulsion.
Colour: Off white
Odour: Faint
Form: Viscous liquid
pH (conc.): 5.0 – 7.0
pH (in-use): 7.0 – 8.5
SG: 1.0 at 20°C

Package & Handling

Fernox Leak Sealer F4 is supplied in 500 ml bottles.

Fernox Leak Sealer F4 is classified as non-hazardous, but as with all chemicals, keep out of reach of children. In case of contact with eyes or skin, rinse immediately with plenty of water.

Volumetrics

Product Code	Single Unit Barcode	Single Unit Dimensions (Depth x Width x Height)	Single Unit Weight(Kg)	Outer Carton Barcode (ITF)	Outer Carton Dimensions (Height x Width x Depth)	Outer Carton Box Weight(Kg)
56603	5014551566033	182 x 88 x 52 mm	0.60	05014551000766	195 x 268 x 182 mm	6.13

Downloads

Fernox UK Catalogue 2025 Q1

Frequently Asked Questions

How to repair system leaks

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.

Can Fernox Leak Sealers be used in combination boilers?

Yes, all Fernox internal leak sealers, such as Fernox Leak Sealer F4, are safe for use with combination and other low water content boilers. They will not block valves or vents. Leak Sealer F4 Express is recommended for all pressurised systems as this can be added in 30 seconds via a radiator, filling loop or Fernox TF1 Filter, without the need to drain the system.

Videos

How does Fernox Leak Sealer F4 work