Fernox F4 Central Heating Leak Sealer Express 400ml

By Fernox Product code: 83815 Pack size: Each

£18.38 was £22.98 Exc. VAT £15.32

Product Details

Seals small leaks and weeps which may cause pressure loss and boiler breakdown.

Suitable to be used throughout a central heating system to seal small leaks and weeps which may cause pressure loss and boiler breakdown. Once dispersed within the system it will be effective 1-24 hours after application. The unique sealing efficiency of this proven product has been specifically developed to prevent blockages or restrictions within the boiler or vulnerable system components such as pumps and safety devices.

• Seeks out and seals inaccessible, internal microscopic leaks fast
• Quick and convenient – doses in 30 seconds - no need to drain down the system
• Non-toxic, environmentally friendly formulation, compressed air propellant and 100% recyclable can
• One 400m canister treats up to 130 litres of system water (16 radiators) and the equivalent of 250m2 of underfloor systems.

Technical Specification
Brand Fernox
Unavailable offshore 1
Manufacturer ID 62422
Type Leak Sealer
Volume (L) 0.4
Volume (ml) 400
Container Type Liquid
Range Name F4
Delivery details

DELIVERY OPTIONS (UK mainland only)

Next Day Delivery – £5.00 or FREE for orders over £35

  • Order before 7pm Monday to Thursday for next business day delivery
  • Order Friday to Sunday before 5pm for Monday delivery
  • Orders placed after Sunday at 5pm will be delivered the following Tuesday
Pre-12pm Delivery – £10.00 to arrive before 12pm on the scheduled days above
Saturday Delivery – £10.00 or £5.00 for orders over £35 & FREE for orders over £75 (order by 6pm Friday)
Sunday delivery – £10.00 or £5.00 for orders over £35 & FREE for orders over £75 (order by 4pm Saturday)
Times may vary for items being delivered directly from the supplier. For more information, please visit our delivery information page below.
Items over 30kg can only be delivered from Monday to Friday. If ordered before 6pm, please allow up to two business days for delivery. Orders placed after 6pm Thursday will be delivered after the weekend.
More about Delivery
Click & Collect details

Collection Details

Our opening times are 7am-8pm Monday-Friday, 7am-7pm Saturday and 9-4pm Sunday. Please check your local branch is open on the branch locator page, before you visit.

Once you have placed your order online, we’ll have it ready for you at the branch you have selected in as little as 5 minutes. We will hold your order for 14 days, after which we will automatically generate a refund to the payment type you used to place the order.

Don’t forget your mobile number – Make sure your mobile number is added so that we can text you when your order is ready to collect. Please wait for your text or email before coming to collect your items.

If an item is eligible for Next Business Day Collection in branch, the order must be placed by 7pm Monday to Thursday for collection the next day. Orders placed after 7pm on Thursday, and up to 5pm on Sunday, will be available for collection on Monday. For larger items over 30kg, please allow two business days.

Fernox F4 Central Heating Leak Sealer Express 400ml is rated 4.6 out of 5 by 56.
Rated 5 out of 5 by from EXCELLENT PRODUCT Excellent stuff, didn't fancy removing my radiator for a minor leak as I don't have the correct key. After reading about this product I decided “nothing to lose” so gave it a go. Brilliant result, leak started to dry up after a couple of hours, and I wouldn't hesitate to use it again. The only problem I had was I didn't drain the radiator down sufficiently, but managed in the end, you need to drain about 2 bucketfulls of water, I know for next time, if there is a next time
Date published: 2022-05-10
Rated 5 out of 5 by from Great service great product Fantastic service my item was with me quickly and did exactly what it said it would
Date published: 2022-05-01
Rated 5 out of 5 by from It works Does what it claims to do. Our system was losing pressure almost twice a day from a slow leak, and our plumbing expert was dithering about this. Should have just got on with it. Do learn how to apply it to a radiator before you do - some decent videos out there.
Date published: 2022-04-19
Rated 1 out of 5 by from The adaptor that came with the can of Fernox did not fit the can, I could only use it because I had an old one The adaptor that came with the can of Fernox did not fit the can, I could only use it because I had an old one
Date published: 2022-04-02
Rated 4 out of 5 by from Quick and easy sealant. Central heating system has been gradually losing pressure so purchased Fernx F4 to seal any air leaks. Easy to use with video assistance and so far so good. Pressurised the system the day after dosing and touchwood the pressure seems to be constant. Fine product.
Date published: 2022-03-29
Rated 5 out of 5 by from Great product Definitely watch video first
Date published: 2022-03-20
Rated 5 out of 5 by from Life saver Been battling with pressure loss for years. Was convinced it was faulty internal expansion vessel so replaced it then added another external expansion vessel and no luck. Two cans of this and we’re good. No issues for over 2 weeks.
Date published: 2022-03-06
Rated 4 out of 5 by from Fernox no filling loop Would have been 5* but does not have an adaptor for a filling loop. Have to use Fernox filter or radiator. I did use filter but it’s a bit fiddly closing of valves flushing filter opening filter snd drain etc. filling loop would have been quicker
Date published: 2021-12-19
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