Rafal Kaczynski
Hi It seems to look like one of your valves is shut off or is blocked . It also can be a sludge in radiator so if it's you would need a plumber to flush your system out. Before you will get a plumber please try to move lockshield valve and TRV a few times ( turn off and on)it may help. If problem won't solve you would need a lumber to check what is causing this problem I am affraid. Best regards Rafal
