The "Sludge" Problem
A radiator that is cold at the bottom usually signifies a buildup of magnetite sludge (iron oxide). As your heating system corrodes internally over time, this heavy sludge settles at the bottom of your radiators, preventing hot water from circulating effectively.
Symptoms of Sludge Buildup
- Radiators cold at the bottom
- Boiler making kettle-like noises
- Dirty/dark water when bleeding radiators
- Some rooms colder than others
The Solution: Power Flushing
Bleeding the radiator won't fix this (bleeding removes air, which causes cold spots at the TOP). To remove sludge, you need a system flush or a localized repair.
Steps you can try:
- Turn off the heating.
- Open the lockshield valve fully (count the turns so you can reset it).
- If flow improves, it might just be a balancing issue.
If that fails, you need a professional to perform a Power Flush or chemical clean. This forces high-velocity water through the system to dislodge the debris.