1. Fernox 56603 F4 Leak Sealer Internal 500ML

    Model: 56603
    Availability: same day dispatch Same day dispatch if ordered before 1:00 pm
    Price:   £19.99

Fernox leak sealer F4 liquid is an ideal solution for reducing pressure loss from sealed systems. 

Fernox Leak Sealer F4 is used throughout domestic heating systems for sealing small, internal, inaccessible leaks. Leak Sealer F4 works best in warm/hot circulating water and once evenly dispersed will usually be effective within 1 - 24 hours. The sealing efficiency of Leak Sealer F4 has been intentionally limited to prevent blockage of safety devices, pumps, etc.


  • Plugs small internal weeps and leaks in central heating systems
  • Ideal for reducing pressure loss from sealed systems
  • Saves time and money on draining down and repairing
  • Treats 100L system or up to 10 single radiators
  • Compatible with all metals and materials commonly used in central heating systems