Fernox F4 Central Heating Leak Sealer 500ml Product Code: 45902

Used throughout domestic heating systems for sealing small, inaccessible leaks. Does not block air vents and pumps.


  • 1 Year Guarantee
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Additional Information
Technical Specification
  • Brand : Fernox
  • Product Type : Central Heating Leak Sealer
  • Volume : 500 ml
  • Model No : F4
  • Pack Size : 1
  • Manufacturer Guarantee : 1 Year Guarantee
  • Pieces in Pack/Case : 1
Product Contents
Delivery & Returns


Standard delivery service up to 3 working days: €8.95

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€19.95 Incl. 23% VAT

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Fernox F4 Central Heating Leak Sealer 500ml is rated 4.6 out of 5 by 34.
Rated 5 out of 5 by from Does what it says on the bottle I had a constant tiny leak that couldn't be found.Always losing pressure on the underfloor heating system and no sign of wet patches anywhere.I used to have to top up system every week or so.I decided to give this a try.I needed 7 or 8 bottles as I have a large system with a thermal storage buffer tank..Its been about 2 years now and still working a treat.I would highly recommend.Just make sure you use enough bottles to cover the volume of water in your heating system..
Date published: 2018-03-02
Rated 4 out of 5 by from Good product Does exactly what it says ,,great product ,easy to you ,,highly recommended
Date published: 2018-02-24
Rated 5 out of 5 by from Does what it says on the tin Great, works every time well worth a try if your losing pressure.
Date published: 2018-01-13
Rated 5 out of 5 by from Fernox Leak Sealer I had a constant pressure drop on my boiler for last 18 months. Boiler recently serviced and nothing visible on boiler or on upstairs radiator. Problem had to be underfloor and just having expensive kardean floors laid didnot want to take up. Tried this product, read the instructions and all looking good. Thanks Screwfix for a great product.
Date published: 2017-11-14
Rated 5 out of 5 by from It works like a charm! I was worried when I saw my pressure dropping down from 1.5 bar to 0.25 bar within 24-48 hours. With no visible leak or discolouring of the plasterboards I was considering the prospect of digging up the floor. I added 2x500ml to my system and hey presto leak fixed!. Pressure on the expansion vessel is now holding firm at 1.25 bar. What great product, can't recommend highly enough.
Date published: 2017-10-18
Rated 5 out of 5 by from Excellent stuff! I recently got my combi boiler replaced but did not change the radiators and pipe work as they were in good condition. The pressure used to drop to 0.8-1.0 bar (from 1.5bar) every 4-5 days and I had to keep topping it up. The company that installed the boiler said the only way to fix it would be to upgrade the microbore pipework as they suspect an issue with the manifold. I dind't want to do this as I have laminate flooring. I decided to give this a shot and it has fixed the leak. It's just been 2 weeks now and the pressure has not dropped at all since adding this. Highly recommended and worth the price.
Date published: 2017-10-07
Rated 5 out of 5 by from Absolutely brilliant I had a pin hole leak on a radiator seam, I had just completely redecorated the room, plastering, new skirts and so on....so was quite upset thinking I had to replace the radiator. Partially drained the system and added 2 bottles to my header tank (circa 18 radiators in my house), then filled up and switched the heating back on. Within an hour the leak has stopped, hopefully it will solve it permanently...
Date published: 2017-09-22
Rated 1 out of 5 by from Boiler Presure Droping Had a leak in heating system thought this would be ideal way to fix it, 5 radiator 1 t/rail 24hrs later, still leaking USELESS STUFF and its not the cheapest Did not work on the last leak either
Date published: 2016-11-20
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