Fernox F4 Central Heating Leak Sealer 500ml

Product Code: 45902
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 Manufacturer's Guarantee
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Safety Data Sheet

Was €21.45

Special Price €18.95

Incl. 20% VAT

Save €2.50 (11%)

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


Standard delivery: €15

Free delivery on all orders over €70.00

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Hopefully you won't need to return an item, however, if you do, it is our aim to make this as simple as possible. By following the guidance below you can help us to help you when a product is not what you expected, or is faulty. Your statutory rights are not affected by this guidance.


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Fernox F4 Central Heating Leak Sealer 500ml is rated 4.681818181818182 out of 5 by 22.
Rated 5 out of 5 by from Excellent product Recommended by my plumber and did not disappoint, was loosing central heating pressure overnight, filled through magna filter and 4 days now and pressure has not budged so worth every penny.
Date published: 2016-06-13
Rated 5 out of 5 by from Brilliant Didn't think this would work or be easy to use, it was both, sealed my leaks, my combi boiler has now started holding pressure - don't think it's ever done that!
Date published: 2016-01-14
Rated 5 out of 5 by from Does what it says ion the tin As a retired plumber with a back injury, i was not too keen to have to drain down my combo boiler system. I had developed 3 leaks and was encountering pressure drops. One from an iso valve gland, one from a lock shield valve and one from the boiler heating feed pipe. I had never used F4 sealer before, and was a little reluctant. I isolated my bathroom towel rail, and removed the top bleed point fitting. I then used a hand siphon to remove just over half a litre of water. I then added the F4 and topped the towel rad back up to the brim. Bleed plug back in and valves re-opened. Less than 5 minutes to complete......DID it work ? Yep, i was well impressed no sign of a leak anywhere after a couple of weeks and pressure is maintained. Recommended.
Date published: 2016-01-02
Rated 2 out of 5 by from Unable to sort leak The boiler engineer has put my boiler pressure vessel on test,but believes I have a system leak. Tried a 1litre bottle of a competitor's leak sealer and it didn't work.Thought I'd try a 0.5 litre bottle of Fernox several day's ago.This hasn't worked either so I haven't found it to be the "magic bullet" that others speak of.Will still have to investigate under the floorboards!
Date published: 2015-11-12
Rated 2 out of 5 by from Doesn't do the job Have a leak under the concrete floor so decided to try this based on the reviews people have written. To start with it wasn't easy to pour into the radiator. Once done and left the heating on for 30 mins and turned off for 24 hours for moment of truth.... Didn't work at all. I was so disappointed. Even if it has worked still I think it's over priced for the quantity you get, at least they could have thrown the gun to pour the liquid into the rad to make the price worth. Didn't work for me hence the low scoring.
Date published: 2015-08-14
Rated 5 out of 5 by from Great product Apart from being a bit tricky to get into the system, this product is amazing!!! I was losing pressure on my combi boiler all the time, not anymore. After 2 days pressure has stabilised and held, very impressed
Date published: 2015-05-31
Rated 5 out of 5 by from top quality overpriced but the best for the job and accepted on all my guarantee requirements for certificates
Date published: 2015-03-29
Rated 4 out of 5 by from Leak sealer Again screw fix has come up with the goods,can not fault the quality of service and value for money .
Date published: 2015-01-17
  • 2016-10-25T07:54CST
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