If your system does not have a filter,then first job would be to fit one,Magnaclean Pro 2 among the best & easiest to fit, the filter will collect any crud dislodge by the cleaner. If a system has not been cleaned prior to use, all of the aforementioned issues for new systems will be present, with the installation debris causing issues and damage to the system.

Sentinel X800 Fast Acting Cleaner into a system? How do I get Sentinel X800 Fast Acting Cleaner into a system?

To complete the cleaning process, you should always drain or flush the system fully to remove all of the debris that Sentinel X800 Fast Acting Cleaner has collected or dislodged. If you do not drain the system of this debris, the system will remain dirty." I located the drain valve just outside the property and opened it to drain the central heating system - left it for about an hour I then opened all of the thermostatic valves on all 7 radiators, turned on the boiler by the mains and turned the temperature up to 25 degrees by the thermostat

If you have a filter fitted, then add some Sentinel X400 to system through the filter & leave it in 2-4 weeks to work,usually see results in just a few hours. Continues bleeding the radiators downstairs, starting with the closet to the boiler until no water or sound could be heard

Removing corrosion/magnetite sludge: Sentinel X400 or x800? Removing corrosion/magnetite sludge: Sentinel X400 or x800?

I’ve been having issues with my radiators not heating up upstairs. I’ve tried everything from bleeding the radiators to balancing them. I am interested to see it because everything else I have read has suggested the system should be flushed out within a few days. A few examples of the kind of debris that can be found in new systems include copper swarf, flux residues, casting sands and rust. Other contaminants can include greases and stamping oils used in the manufacturing process, sometimes applied excessively. When introduced into a central heating system, these materials can cause problems such as corrosion. DS40 is fine for everything apart from Primatic cylinder or an aluminium heat exchanger in the boiler.Sentinel X800 Fast Acting Cleaner can be added to the system in a number of ways. For open vented systems, dose via the expansion tank during the final fill. For empty sealed systems, add to any convenient point before filling. For full sealed systems, use a Sentinel Dosing Vessel to inject via the filling loop or other access point. It can also be dosed through a powerflushing machine.