# Fernox Leak Sealer F4 – 500ml

Leak Sealer F4 is an internal leak sealer designed to quickly seal small, hard-to-reach leaks and weeps within a central heating system, preventing pressure loss and potential boiler failure. Once introduced into the system, the product targets areas where oxygen ingress occurs, forming a polymer to seal pinholes. Effective within 1 to 24 hours of application, this high-performance water treatment is proven to be safe, without causing blockages or restricting flow in vulnerable components such as boilers, pumps, and safety devices. Leaks can be sealed efficiently, eliminating the need for a full system drain down.  

-   Ideal for reducing pressure loss in sealed systems
-   Quickly seeks out and seals internal, microscopic leaks
-   Saves time and money by avoiding system drain downs and expensive repairs
-   Safe to use – does not cause blockages or damage to pipework, pumps, air vents, or heat exchangers
-   Designed for permanent use in the system – compatible with all metals, including aluminium
-   One 500ml recyclable bottle treats up to 130 litres of system water (16 radiators) or 250m² of underfloor heating

## Details

- **Price:** 22.33 GBP
- **Vendor:** FERNOX
- **Type:** Consumables
- **Tags:** Consumables, Heating Protection, Local, Plumbing & Heating

## Variants

| Variant | Price | Available |
|---------|-------|-----------|
| Default Title | 22.33 GBP | In stock |

## Images

- Fernox Leak Sealer F4 – 500ml

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> Source: [Carvers Building Supplies](https://www.carvers.co.uk/products/fernox-leak-sealer-f4-500ml-56603)
> Updated: 2026-06-16