Great product to seal central heating, if you suffer from a very small leak. Pressure now good on the boiler. Lacks instructions, which you probably need to use the Internet, if you haven't used it before. But it's very easy to use, once you know how.
Verified purchase: Yes | Condition: New
Used to have to top up my heating system weekly, but was unable to find any visible leaks. 2 weeks after adding F4 pressure has not dropped.
Verified purchase: Yes | Condition: New
I was disappointed that I couldn't use it via the filling loop, I have been able to do that in the past. In the end I applied the sealer via the radiator bleed valve opening, which was a bit messy when I removed the can from the radiator, so be prepared! Having said that, the product has done a brilliant job!
Verified purchase: Yes | Condition: New
We found the leak! But will still be putting this into our rather old system.
Verified purchase: Yes | Condition: New
Worked well for me where I was weekly loosing system pressure and having to top-up with water via the filling loop to regain the correct pressure to keep the boiler working. I consider the price of Fernox Express F4 Leak Sealer 400ml very reasonable, especially when compared with a boiler engineer call out fee and/or the cost and inconvenience of lifting the floor boards to find a seep.
Verified purchase: Yes | Condition: New
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