Diagnosis: Magnetite sludge settling at the base of the radiator.
Local Factor: Microbore pipework common in Leicester homes blocks easily.
Resolution: Chemical flush (minor) or Power Flush (severe). Bleeding will NOT work.
Need this fixed properly?
Gas Safe diagnostics in Leicester. No guesswork, no upsell.
Why is the radiator cold at the bottom?
The “Air” Myth: Do not bleed this radiator. Air rises. If the top is hot and the bottom is cold, you do not have air — you have sludge.
The black material inside heating systems is Magnetite, a heavy iron oxide sludge formed by internal corrosion. Because it is heavier than water, it settles at the bottom of radiators.
As magnetite accumulates, the flow is restricted, creating a pyramid of cool water. Hot water enters at the top but cannot circulate through the base properly.
The Leicester Microbore Problem
Many Leicester homes built during the 1980s and 1990s — particularly in Oadby estates — were installed with microbore pipework (8mm or 10mm).
Microbore systems block far more easily than 15mm copper because even small amounts of magnetite dramatically reduce flow.
Diagnosis: Cold Top vs Cold Bottom
| Symptom | Physical Cause | The Fix |
|---|---|---|
| Cold top / Hot bottom | Air trapped | Bleed via bleed nipple |
| Cold bottom / Hot top | Magnetite sludge | Power Flush or chemical flush |
| Cold all over | TRV pin stuck | Free pin or replace TRV |
Want a proper diagnosis?
If radiators are cold at the bottom, bleeding won’t help. A short on-site check confirms whether sludge, a stuck TRV, or circulation issues are the real cause.
Book a diagnostic visit⚠️ Stop guessing and turning things up
Increasing the boiler temperature will not remove sludge. It only increases gas usage and stresses the system.
Balancing with Lockshields before cleaning simply moves magnetite from one radiator to another.
Radiators cold at the bottom?
That’s magnetite sludge. Bleeding won’t fix it — cleaning the system will.
Get a power flush quote