There is nothing quite as frustrating as walking past a radiator that is stone cold while the boiler is firing away like a jet engine. You’ve bled the radiators, balanced the system, and still, one room feels like a walk-in freezer.
The likely culprit? A blockage in your central heating pipes.
Turn off the boiler and let the system cool completely (2-3 hours). Step 2: Attach a garden hose to the lowest drain cock (usually on a ground floor radiator). Step 3: Open the bleed valve on the highest radiator to let air in. Step 4: Open the drain cock. Let the dirty water run out. Watch for sputtering—that’s sludge chunks exiting. Step 5: Close the drain cock, refill the system, run it for 30 minutes, and drain again. Repeat until the water runs clear. Method 3: Chemical Unblocking (The "No Tools" Method) For slow circulation issues, chemicals can dissolve soft sludge.