Radiator cold at the bottom, warm at the top
Cold at the bottom is sludge, not air. Bleeding will not fix this one.
What it actually means
Rust and debris (the trade calls it sludge) is heavier than water, so it settles along the bottom of radiators and blocks the flow. Result: warm top, cold bottom stripe.
It builds over years in systems without inhibitor chemical or a magnetic filter, and it quietly makes your boiler work harder and your bills bigger.
Try this first, before you spend a penny
- 1
Confirm the pattern
Cold along the bottom of one or more radiators while the top is hot. That is sludge, not air, and bleeding will not help.
- 2
Check which radiators are hit
One radiator might be isolated and flushed alone. Several means the system needs treatment.
When it is a pro job
Removing sludge properly means a chemical clean or a powerflush and ideally a magnetic filter fitted so it does not come back. That is a pro job with pro kit.
Heating engineer
Typical UK range for a full system powerflush depending on the number of radiators. A single radiator flush or a chemical clean costs less; a filter adds roughly £100 to £150 fitted.
£300 to £700
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