F4 Express Leak Seal 265ml aerosol

It is 5 months since I used this product and it has worked perfectly. I used to have to top up my boiler every few weeks by a bucket or so, since I used this product I have not topped up in five months and the display shows 1.0 pressure all the time. I don't normally bother to write reviews very often but I am so pleased with this purchase I am pleased to write a review. I just wished I had used this years ago as I dread to think what all those countless gallons of water has done to our underfloor foundations and damp problems. Thanks Fernox.

Didn't need this second product, first one purchased is still going strong.David

Great product, saving for my summer project as don’t want to tempt providence until then. Comes with all the required spots so will be easy to add to the heating system.

So far so good. However the instructions are a little vague. And small to read on tin. A couple of reviews on here mentioned when putting into a radiator that they ended up with a cold spot where inserted. Spoke to a plumber and he told me after insertion start boiler on lowest temp to circulate it for 15 mins. Then up the temp to max for 30 mins. These products are heat activated so if you start with it too hot it sets before distributing through system.

The nozzle broke halfway through using so the leak seal came streaming back out of the radiator and blocked the bleed valve enough to prevent the bleed screw to be inserted back in. So made matters worse and now I can only bleed half the radiator as a result very unhappy with the result.

Does exactly what it should! Quick and easy to use, very pleased.

Done the job and has sealed the system and there has been no drop in pressure since it was used. Can't comment on the applicator as the boiler was being serviced by the engineer and he chose to remove a small radiator and apply through that. Very pleased though with the result.

My 45 year old heating system had a leak, presumably from the pipes under the concrete floor screed since all visible valves and connections, and the boiler, had been checked. This was a last-ditch attempt at fixing the pressure drops before committing to a £2000+ re-pipe with surface mounted drops form the attic. I was a bit worried about the boiler, since it is still in warranty, but took the chance.I made sure that everything was completely cold before starting, bled all radiators, turned off all but one of the radiators. I have a Fernox TF-1 filter under the boiler, and so I used this as the dosing point. This was very simple - basically close the isolation valves both sides of the TF1, open the bottom to drain it out into a bucket, remove the bleed valve from the top, and then squirt the F4 sealant into the bleed hole. I ran the system on its lowest temperature (30C) for a couple of hours, then I ramped it up to full (75C) for 24 hours, then back down to 30C for 24 hours, completely off for 24 hours, and then repeated the process with all radiators on. This gave the sealant plenty of chance to mix well with the water, and also for the pipes to expand/contract and open any small cracks in joints.So far so good. The pressure has held for a week so far, whereas previously it was losing 0.1 to 0.2 bar per day. I'm sure it's not going to be a long-term fix, but seems to be doing the job for now.