Yes, all Fernox internal leak sealers, such as Fernox Leak Sealer F4, are safe for use with combination and other low water content boilers.
They will not block valves or vents. Leak Sealer F4 Express is recommended for all pressurised systems as this can be added in 30 seconds via a radiator, filling loop or Fernox TF1 Filter, without the need to drain the system.
One litre of water weighs 1 kg, therefore 2 kg of DS40 System Cleaner per 100 litres of system volume will make a 2% solution.
If the dip test shows less than 100ppm, installers can immediately resolve the issue by adding a high-quality inhibitor such as Fernox Protector F1 or where a filter is fitted, Protector+ Filter Fluid. The test can be re-taken once the inhibitor has circulated to confirm the level has been met.
Make sure the system is turned off and allow radiators to cool down (1). Select a radiator and shut both the wheel-head and lock shield valves (2). If a thermostatic radiator valve (TRV) is fitted, close it by turning it to the minimum setting. Having removed the air vent pin using a cloth to absorb any escaping water (3). Screw
