Radiator cold at the bottom, warm at the top
🔒 Written by a Gas Safe registered engineer
May Need Pro💷 £80–£600⏱ 5 min
⚠️
This job may need a professional
Check the steps below first — if you\'re not confident, get it fixed safely today.
Find a Gas Safe engineer near you →Not sure if this matches your problem?
Use our interactive tool — answer a few questions and get a personalised diagnosis.
Most likely cause & what to check
1
Feel the radiator — if it's hot at the top and cold at the bottom, this is sludge (black iron oxide) settled in the base. It's not something you can fix yourself.
2
Check if more than one radiator has this problem — if so, the whole system is affected.
3
Call a heating engineer. Tell them: "One or more radiators are warm at the top but cold at the bottom — I think it's sludge and the system may need a power flush."
Want this sorted today by a professional?
Find a local engineer →Find a Gas Safe registered engineer near you and get it fixed properly.
Was this guide helpful?
More guides in Radiators
Radiator not getting hot at all
Radiator stays completely cold when heating is on
Replacing a radiator valve
Leaking or faulty radiator valve needs replacing
Radiator cold at the top, warm at the bottom
Top of radiator stays cold when heating is on
TRV stuck — radiator won't heat up or won't turn off
Thermostatic radiator valve stuck open or closed