One Radiator Cold? The Top-or-Bottom Check Before You Bleed It, by DGN GAS on YouTube. 3 min 37 s.
- Video length
- 3 min 37 s
- Time to do it
- 10 minutes
- Difficulty
- Easy
- Steps
- 8
What you need
Steps
Turn the heating on and let it run until the other radiators in the house are hot. This gives you a fair comparison.
Put your flat hand on the cold radiator, first at the top and then at the bottom. Note which part is warm and which is cold.
If the bottom is warm and the top is cold, the radiator has air in it. This is the one case where bleeding helps.
If the top is hot and the bottom is cold, the problem is sludge or a stuck valve, not air. Do not bleed it. Call a heating engineer.
If the radiator is cold all the way across while the rest of the house is hot, the valve is likely closed or the radiator is not getting flow. Check both valves are open before anything else.
For an air-filled radiator, open the bleed valve at the top with the key. Hold a cloth under it and close the valve as soon as water runs steadily instead of hissing air.
Go to the boiler and check the pressure gauge. If bleeding dropped it below the maker's range, top it up with the filling loop to the correct cold pressure.
If you have to bleed the same radiator every few weeks, stop and get the system checked. Repeated air usually means a leak or a pump problem.
Tips and common mistakes
Bleeding a radiator lowers system pressure, so always check the boiler gauge afterwards.
Never bleed a radiator when the system is cold and running at high pressure, and keep the cloth ready for drips.
If you are unsure what the cold pattern means, call a Gas Safe registered engineer rather than guessing.
Questions
Why is only one radiator cold when the rest are hot?
It is usually air, sludge or a closed valve. Feeling the top and bottom tells you which one you have before you touch the bleed key.
Do I need to top up the boiler after bleeding a radiator?
Often yes. Bleeding releases water and air, so check the pressure gauge and refill with the filling loop if it has dropped below the maker's range.
Can I bleed a radiator that is hot at the top and cold at the bottom?
No. That pattern points to sludge or a valve issue, not air, and bleeding will not fix it.
This guide was drafted from the video's details and general task knowledge. It has not been checked against the full video. Check the video and relevant product instructions before following a procedure. Report a correction.
