Why is my radiator cold at the bottom?
I see this with older heating systems. Over time, rust and magnetite sludge builds up inside the radiator, settles at the bottom and stops the hot water circulating through that section. Bleeding usually won't fix it. Depending on how bad it is, you might need a radiator flush or a system clean.
Why is my radiator cold at the top?
That is usually air trapped inside the radiator. It sits at the top and stops hot water filling that part. You can often sort it by bleeding the radiator with a radiator key, with the heating off and the radiator cooled down first.
Why is the whole radiator cold?
Check the basics first. Is the radiator valve turned on? Is the thermostatic radiator valve (TRV) stuck? Could the system need balancing? If several radiators are cold, I'd also look at the boiler, circulation pump and system pressure, depending on the type of heating system you've got.
Should I replace a cold radiator?
You don't want to start spending money replacing radiators when the problem might be something simple.
The temperature pattern is a useful clue, but I'd also want to know whether it's one radiator or several.
What can I safely check myself?
- Check the valves: Make sure they're open.
- Compare radiators: See whether the problem affects one room or the whole house.
- Listen for gurgling: That can indicate air in the system.
- Don't keep bleeding radiators repeatedly: If air keeps returning, there may be another underlying issue. Check your boiler manual before adjusting system pressure.
If the radiator is hot at the top but cold at the bottom, I'd suspect sludge first, but I'd confirm the circulation problem before recommending a flush.