Browse store

Fernox Central Heating Leak Sealer F4 500ml (45902)

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

More Info

£16.99INC VAT (£33.98/Ltr)

Add to basket for...

Rated 4.5 out of 5 by 14 reviewers.
  • 2016-05-03 T06:58:51.315-05:00
  • bvseo_lps, prod_bvrr, vn_prr_5.6
  • cp-1, bvpage1
  • co_hasreviews, tv_14, tr_14
  • loc_en_US, sid_45902, prod, sort_default

Add to saved list...

Save
Rated 5 out of 5 by 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! 14 Jan 2016
Rated 5 out of 5 by 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. 2 Jan 2016
Rated 2 out of 5 by 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! 12 Nov 2015
Rated 2 out of 5 by 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. 14 Aug 2015
  • 2016-05-03 T06:58:51.315-05:00
  • bvseo_lps, prod_bvrr, vn_prr_5.6
  • cp-1, bvpage1
  • co_hasreviews, tv_14, tr_14
  • loc_en_US, sid_45902, prod, sort_default
Page : 2 next>
3 Questions  4 Answers

Screwfix Q&A

Ask your questions. Share your answers.

 
 
« Back
 
 
Search:
Sort by:
My plumber added 500ml of Fernox F4 to my CH system to stop a leak and loss of boiler pressure. This worked for about 3 weeks, now we have a very slight loss again. We have 15 radiators and I note that 500ml is designed for up to 10 rads. Should I add another 250ml, or start again and add 750ml ??
16 Mar 2016
Customer avatar
by
Portsmouth
Read all my Q&A
, DIY
0points
0out of 0found this question helpful.
Was this helpful?Yes0No0

Answers

Answer: 
Definitely. One bottle per 100 litres of water in system or roughly 10 radiators. It only workd on my 26 radiators after the 3rd bottle. The manufacturer says it won't clog pumps. I never had any problem.
28 Apr 2016
Customer avatar
by
London
Read all my Q&A
, Builder/Multi Trade
0points
0of 0found this answer helpful.
Was this helpful?Yes0No0

Best answer
Answer: 
Hello Twodogs,

Thanks for your question. Unfortunately, as you have a larger (15 radiator) system, using 500ml has under dosed your system, which is why the problem has come back. In order to fix this you should re-dose using two 500ml bottles of the F4, in order to cover your whole system.
17 Mar 2016
+4points
4of 4found this answer helpful.
Was this helpful?Yes4No0
9 Nov 2015
Customer avatar
by
southminster
Read all my Q&A
, DIY
0points
0out of 0found this question helpful.
Was this helpful?Yes0No0

Answers

Answer: 
Hello Edwardy. If you have no expansion tank the best option would be to dose using the F4 Express (61837) as this is designed to go straight into your radiator, rather than an expansion tank.

If you have already purchased the 500ml version, you can either through go through a system filter, such as the TF1 Total Filter, or you can dose using a small funnel to pour into a radiator bleed valve.
10 Nov 2015
+7points
8of 9found this answer helpful.
Was this helpful?Yes8No1
10 Sep 2015
Customer avatar
by
east sussex
Read all my Q&A
, DIY
0points
0out of 0found this question helpful.
Was this helpful?Yes0No0

Answers

Answer: 
Hello Diy4Den, these two products are compatible.
3 Nov 2015
+2points
2of 2found this answer helpful.
Was this helpful?Yes2No0
1 of 1
  • 2016-05-04 T06:32:47.878-05:00
  • bvseo_lps, prod_bvqa, vn_prr_5.6
  • cp-1, bvpage1
  • co_hasquestionsanswers
  • loc_en_US, sid_45902, prod, sort_default
1 of 1
Specification
Brand Fernox
Colour Green
Model No F4
Pack Size 1
Pieces in Pack/Case 1
Product Type Central Heating Leak Sealer
Sealant Adhesive Volume 500 ml
Total Product Weight 572 kg

Downloads

Safety Data Sheet (COSHH)