Why is my radiator hot at the top but cold at the bottom?

Yeah, sounds like you’ve got sludge in the bottom of the radiator. If it’s hot at the top but cold at the bottom, bleeding it won’t fix it – that’s more for when there’s air trapped, which usually stops the whole thing heating up properly.

What I’d do is shut off both valves, take the radiator off the wall (have a tray or some towels ready – it gets messy), and flush it out with a hose. You’ll see all the gunk come out, and that should sort it.

If it’s not just this one radiator, it might be worth lookin’ into a system power flush, and don’t forget to add inhibitor to stop it building up again. Shouldn’t be too hard to sort – good luck!

If it’s hot at the top and cold at the bottom, it’s most likely sludge build-up rather than air in the system. Bleeding won’t help in this case, as that’s only for trapped air which usually stops the whole radiator from heating properly.

You’ll need to flush the radiator to get rid of the sludge. Turn off the valves, remove the radiator, and give it a good rinse out with a hose. You’ll see all the muck come out, and that should fix the issue. If you’ve got the same problem across multiple radiators, it might be worth getting a full system flush to clear everything out. Also, adding inhibitor afterwards can help stop it happening again.

That’s sludge build-up, not air. Bleeding won’t help since the top is already heating fine. You’ll need to flush the radiator – turn off the valves, take it off the wall, and rinse it out with a hose. If it’s happening across multiple radiators, a system power flush might be worth considering. Add inhibitor after to prevent it building up again.

DD