Leaking Radiator? Where It's Coming From and What to Do
Valve, spindle, tail or the panel itself, each one leaks differently, and only one of them means a new radiator.
Find the actual source first
Dry everything completely, then lay kitchen roll at four places: under the valve on each side, around the spindle where the head screws on, and along the bottom seam of the panel. Come back in an hour. Whichever paper is wet tells you which of four very different jobs this is, and they range from a 50p olive to a new radiator.
A weeping valve or nut
The most common and the least serious. The compression nut where the valve meets the tail has loosened or the olive has hardened. A quarter turn with two spanners, one holding the valve body so you do not twist the pipe, stops most of them. If it still weeps, the olive needs replacing, which means draining down.
A leaking spindle
Water appearing from under the plastic head when the valve is turned is a failed gland. Some valves have a gland nut you can nip up; many modern ones do not and the valve gets replaced. Either way it is a valve job, not a radiator job.
A pinhole in the panel
A rust-coloured weep from the bottom of the panel itself is corrosion from the inside out, and there is no repair worth having. Sealant additives buy weeks, not years, and they can clog the boiler while they do it. This one is a replacement radiator, and the cause is usually system sludge from missing inhibitor.
Stop it now, then deal with it
Close both valves, the thermostatic one and the lockshield at the other end, counting the turns on the lockshield so it goes back to the same balance point. That isolates the radiator without draining the system. Bowl underneath, towels down, and it will hold until an engineer arrives.
Why it matters more than it looks
A slow radiator leak drops system pressure, so the boiler gets topped up with fresh oxygenated water again and again. That oxygen is what corrodes the rest of the radiators. One weeping tail ignored for a year is how a whole system fills with sludge.
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