F4 Leak Sealer 500ml Liquid Seal for Central Heating Pipe Work Leaks Water Underfloor Heating Non-Corrosive Non-Toxic Compatible with Most Heating Systems Long-Lasting Seal

Tried a cheaper make it stoppes a little bit, but was losing halve a pound pressure a week, drained the water filter on my Worcester oil boiler put 500ml in and maintained pressure 1 month now

Over the years I’ve had a few of these and its worked for me stopping those annoying hard to fine leaks in the heating system. I always keep a spare one handy just in case the boiler starts to drop pressure regularly.

Definitely stops leaks but only seems to last for 8 to 12 months. So, a new application is required annually - not a big problem, as it’s probably as good as it gets regarding leak prevention in a radiator system.

Had a slow system leak. I checked all the radiators, ceilings and any exposed pipework. Nothing! My worse fear, it looked like a slow leak in the pipework laid in the concrete on the ground floor back in 1972. F4 Leak Sealer purchased and within a few hours the pressure was holding again. It's been a week now and we're still good. Most impressed. Would happily recommend.

This company been around for years. Always used a range of products. Good results. Plumber for 44 years.

This product is excellent at sealing small weeping joints in an old system

Seems to have fixed a leak I couldn't fix for the last 10 years!

Solved a pressure loss problem that was unable to be located. Since installation, four months now, our system pressure has not had to be topped up once.

Funktioniert super und sofort. Absolut dicht.

Funciona. Tenía una fuga que me hacía perder (casa unifamiliar 3 plantas) 0,1bares de presión por día. Cada 3-4 dias tenía que rellenar el circuito. Al no encontrar humedades y tras revisión de la caldera, me decidí por Fernox. Lo puse en un radiador de la ultima planta, calefacción a tope durante 5 horas y luego uso normal el resto de días. En menos de 2 días ya notaba que no perdía nada. Ahora a ver lo que dura!

Ottimo prodotto per ora mantiene quello che dice, provato su vaso aperto di termocucina a legna.

Super produit J'ai réparé une chaudière sur laquelle aucune soudure ne tenait plus. Même les plombiers sui ont échoué m'ont demandé la référence, Attention produit efficace pour les microfissures fuites à coupler avec un mastic haute température

I don't normally write reviews, let alone positive reviews. I have a 25 year old heating system with 14 radiators that was losing pressure, so much that I had to top it up twice a week, yet I could not see any obvious leakage - except there was one unexplained slightly damp area on a wall near some of the pipes. I was going to open the wall to investigate, then I thought I'd give this a try, just in case it helped to reduce the leak until I could find the time to investigate properly. I was very skeptical. Well, nearly 8 weeks later, and absolutely no drop in pressure. The damp patch on the wall has dried out, so I know where to look in the future if I ever want to fix it properly - let's see if it holds, but for now, the problem is 100% solved - unbelievable.