Fernox Express Leak Sealer F4 265ml

5 reviews

£34.91 (Inc. VAT)

Estimated Delivery: 2 - 7 Days


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F4 Leak Sealer Express from Fernox is suitable for use throughout a heating system for sealing small weeps and inaccessible leaks. It works best when you have circulating hot or warm water in the system and it’s usually effective within 1 to 24 hours after use.

Safety devices, pumps and other similar parts will not be blocked while in use.

One 265ml can is suitable for approximately 10 single radiators or an average sized heating system and is added via a filling loop or a radiator.


Features and Benefits:

  • Doses in 30 seconds making this one of the fastest leak sealers on the market.
  • No mess makes this product a breeze to use.
  • Supplied with a filling loop, or alternatively can be added directly into a radiator.
  • No need to drain down your central heating system which saves you money.
  • Seeks out to seal most leaks and weeps.
  • Environmentally friendly formulation in a 100% recyclable can
  • 265ml can
CE Approved

Fernox Express Leak Sealer F4 265ml Video


Fernox Express Leak Sealer F4 265ml

£34.91 (Inc. VAT)

Estimated Delivery: 2 -
7 Days

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5 Product Reviews

  • Keith Wadsworth
    5/ 5

    Have had a difficult few months with low pressure causing the central heating to fail to start in a morning. First problem was to do with the boiler, which was solved by the service engineer, and the problem stopped being daily but was still there about every three days. The engineer suggested this product as he was convinced there was a leak hidden somewhere in the pipework. Since applying we have had no problems at all. Really pleased. Such fast delivery as well. Thanks.

  • Lauryn Andrade
    5/ 5

    Follow instructions carefully if using via radiator to avoid a mess on the floor. Make sure rad valves are closed before removing vent and that a valve is open after attaching tube and before injecting the product and closed again before removing the tube. Obvious but worth taking care. After about 4 weeks there is no pressure drop in the system at all. It took a few days to work but it seems to have fixed my problem.

  • Al
    5/ 5

    Best price and fast delivery None cheaper or quicker

  • Colin Houghton
    4/ 5

    I've used this product several times as a handyman and it did the job well. However I found that injecting it through a rad air vent was potentially messy. You need to ensure that the pointed nozzle is a good fit after you screw it in and also keep a rag around it to soak up any spillage. Nowadays, my preferred method is to inject it through the radiator vent plug using the 1/2 inch BSP threaded adapter. Even that method can result in small leak backs. To ensure a good seal, I now fit a suitably sized "O" ring over the adapter. Of course, I realise that not everyone has an "O" ring kit to hand..ha.ha! If you can get a good seal using an "O" ring the added advantage is that you can leave the F4 canister in place whilst you open up the rad valves and fire up the circulation pump. That moves the sealant around. After 5 minutes, you then stop the circulation, close both rad valves and remove the F4 canister. Then you put back the radiator vent plug and turn on the central heating. Alternatively, if you follow Fernox's instructions to remove the F4 canister before you open up the rad valves and restart circulation, you will find that a lot of their expensive sealant oozes back out of the rad :(

  • Graham Truman
    4/ 5

    We have not used it yet, waiting for the plumber to come and service the boiler, then he can put the F4 in the system then we shall be good to go as they say. But I am very satisfied with the service and delivery of the fernox.