Radiator Cold at the Bottom but Hot at the Top? Here's Why
If you have run your hand across a radiator and found it warm across the top but stone cold along the bottom, you are looking at one of the most common heating faults in UK homes. It is almost always caused by sludge, and it is very fixable.
What causes a radiator to be cold at the bottom
Over the years, the water circulating around your central heating slowly corrodes the inside of your radiators and pipes. That corrosion creates a thick, black, muddy residue called sludge, or magnetite. Because it is heavier than water, it sinks and settles along the bottom of your radiators.
As the layer of sludge builds up, hot water can no longer reach the lower part of the radiator. The top still heats because water flows across it, but the bottom stays cold. The bigger the sludge deposit, the larger the cold band along the base.
How to tell sludge apart from trapped air
Trapped air collects at the top of a radiator, so if the top is cold and the bottom is warm, the fix is usually to bleed it. Our guide on how to bleed a radiator walks you through that. Cold at the bottom is the opposite problem and bleeding will not help, because the issue is solid debris, not air.
Can you fix it yourself?
You can try turning the radiator off, removing it and flushing it through with a hose outside, but on a system full of sludge the problem usually returns within a season because the rest of the pipework is still contaminated. To clear the whole system properly and stop it coming back, the reliable answer is a power flush.
How a power flush fixes it
A power flush pushes a high flow of water and cleansing chemicals through every radiator and pipe, breaking up and carrying away the sludge that has settled. The system is then refilled with clean water and a corrosion inhibitor that stops the sludge reforming. Radiators heat evenly again, top to bottom, and your boiler stops straining against blocked pipework.
We carry out power flushing across Sunderland, Durham, Washington and the wider North East, with fixed pricing from £495 including VAT. If one cold radiator has turned into several, it is worth acting before your boiler starts to suffer too.
Request a free quote or call us on 0191 540 2051 and we will check whether a flush is the right fix for your system.