Fernox F4 Central Heating Leak Sealer Express 400ml

By Fernox Product code: 83815 Pack size: Each

£24.78 Exc. VAT £20.65

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 £25

  • Order before 9pm 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 £25 & FREE for orders over £75 (order by 6pm Friday)
Sunday delivery – £10.00 or £5.00 for orders over £25 & 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-6pm Saturday and 9-4pm Sunday. Please check your local store is open on the store locator page, before you visit.

Once you have placed your order online, we’ll have it ready for you at the store 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 store, the order must be placed by 9pm Monday to Thursday for collection the next day. Orders placed after 9pm 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 4.5 out of 5 by 75.
Rated 5 out of 5 by from Quick and simple Really easy to use (filling loop on system). Will buy again if neeedd.
Date published: 2023-03-14
Rated 5 out of 5 by from So far so good Only added this a week ago but so far it seems to have stopped my boiler losing pressure gradually the only thing I would say is drain a little water from your radiator before adding or it does tend to spill back out
Date published: 2023-02-28
Rated 5 out of 5 by from Wonderfull and easy application. It was so easy to aplly. All sorted within a few minutes. Great item and worked well. Highly recommended to anyone.
Date published: 2023-02-15
Rated 3 out of 5 by from Not so Express but sealed non the less It wasn’t express for me! Somewhere under the floorboards I had a micro leak on the pipework on one of three downstairs radiators, a drop of approx 1 psi per day, it took two cans to seal it off, 1st can had little if no effect. I used the 2nd can with all the first floor rads shut off, therefore concentrating the solution to the downstairs rads. After a second lot of three 1.5 hrs stints of running the heating, I finally could not detect a drop over a 24 hr period now with all rads back in service. NB it cost almost as much in gas as the two tins of sealer, maybe we should all rip our central heating out and go back to burning wood and coal?
Date published: 2023-02-09
Rated 4 out of 5 by from Good product, but could do with more application guidance. Product does the job - but needs some consideration nin application, Firstly, use it before you repressurise the system, and if the system has been filled before applying, lower the pressure. The methods of application work fine if there is no real pressure in the system, but may not if they are fighting against normal pressure. Once in the system, the Fernox F4 does what is says on the tin. Have used on two or three systems, all without problem after use.
Date published: 2023-02-08
Rated 4 out of 5 by from Open the filler loop isolator. Seems obvious but instructions are non existent. Filling by filler loop is easy, you connect up, squeeze and boom the pipe comes off and foam everywhere. Then it's its the realisation you hadn't opened the the loop isolator. Once opened it all works great.
Date published: 2023-01-22
Rated 4 out of 5 by from No staff. Poor Waited 20 mins to be served as no staff. Never again
Date published: 2023-01-02
Rated 5 out of 5 by from Central heating leak sealer Very easy to use. Seems to have worked.
Date published: 2022-12-09
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