A radiator leaking at the valve usually comes from worn packing, a loose gland nut, or a failing thermostatic valve, not the radiator body itself.
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Quick answer
A radiator leaking at the valve, rather than from the radiator body itself, usually traces back to worn packing material or seals around the valve's spindle, a loose gland nut that can sometimes simply be tightened, or a failing thermostatic radiator valve (TRV) whose internal seal has degraded with age. Identifying exactly where on the valve the water is coming from is the key diagnostic step, since the fix differs depending on whether it's the spindle, the union connection, or the valve body itself.
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A radiator valve has several potential leak points: around the spindle where it enters the valve body (often controlled by a gland nut and packing), at the union nut connecting the valve to the radiator, or at the compression fitting connecting the valve to the pipe. Wiping the area dry and then watching closely as the system runs, or dabbing with a dry tissue at different points, helps narrow down exactly which connection is weeping before assuming the whole valve needs replacement.
A leak that only appears when the valve is being turned (opened or closed) versus one that's constant regardless of valve position also points toward different causes, the former often being the spindle packing and the latter more likely a union or fitting issue.
The gland nut and packing material around a valve's spindle are designed to seal against water while still allowing the spindle to turn to open and close the valve, and that packing can dry out, compress, or wear over years of use, particularly on an older valve that's been repeatedly operated. In some cases, simply tightening the gland nut slightly resolves a minor spindle leak, though over-tightening can make the valve stiff or hard to turn, so it's a careful adjustment rather than cranking it down hard.
If tightening doesn't resolve it, the packing itself may need to be replaced, which is a more involved job, or the valve may simply be at the end of its service life and due for full replacement.
A TRV has an internal element that expands and contracts with temperature to automatically adjust flow, and beyond the same spindle and packing concerns as a manual valve, a TRV can also develop leaks or erratic behaviour if its internal mechanism itself has degraded. A TRV that leaks and also seems to no longer respond properly to its dial setting is more likely due for full replacement than a simple repackaging.
TRVs are generally straightforward to swap on their own, since the underlying valve body and isolation typically stay the same, but confirming the leak is actually the TRV head and not the valve body underneath it matters before replacing the wrong part.
| Leak Location | Likely Cause | Typical Fix |
|---|---|---|
| Around the spindle | Worn packing or loose gland nut | Tighten gland nut; replace packing if needed |
| Union nut to radiator | Worn washer or loose connection | Re-seat with new washer, retighten |
| Valve-to-pipe fitting | Compression fitting issue | Reseat or replace fitting |
| TRV head itself | Degraded internal seal or mechanism | Replace TRV head, often without disturbing the valve body |
This table is a starting point for narrowing down the likely cause, not a substitute for actually inspecting the specific valve, since more than one of these issues can sometimes be present at once, especially on an older system.
Any repair at a radiator valve involves working on a component under system pressure and connected to a shared boiler loop, so isolating that radiator correctly before loosening anything matters, and a mistake can mean a bigger, uncontrolled leak rather than a small manageable one. If the radiator lacks isolation valves, or if you're not confident diagnosing exactly which part is the source, it's worth having a technician assess it rather than guessing.
Radiant and radiator loops share water (and often pressure) with a natural-gas boiler, so changes to the boiler's fill pressure, relief valve, or combustion venting are not homeowner work. That belongs to a Technical Safety BC licensed gas fitter. CANRO holds gas licence LGA0043870 and boiler licence LBP0046450. If you ever smell gas near the mechanical room, leave the house first and call FortisBC's emergency line, 1-800-663-9911, from outside.
Safety note
Radiant and radiator loops share water (and often pressure) with a natural-gas boiler, so changes to the boiler's fill pressure, relief valve, or combustion venting are not homeowner work. That belongs to a Technical Safety BC licensed gas fitter. CANRO holds gas licence LGA0043870 and boiler licence LBP0046450. If you ever smell gas near the mechanical room, leave the house first and call FortisBC's emergency line, 1-800-663-9911, from outside.
A gentle tightening of the gland nut around the spindle sometimes resolves a minor leak, but over-tightening can make the valve stiff or damage it, so a light, careful adjustment is worth trying before assuming a full repair is needed.
Often the underlying valve body and packing concerns are similar, but if the TRV head itself has failed internally, the fix is usually replacing the head rather than repacking a spindle.
No, in most cases the radiator body itself is fine and only the valve, or a specific part of it, needs attention.
A leak that appears specifically when operating the valve often points to worn spindle packing, since that's the seal being disturbed by turning, rather than a static connection like a union or fitting.
If the radiator has its own isolation valves, you generally only need to isolate and drain that radiator locally, not the whole system, which is one good reason to have isolation valves added if your radiators don't already have them.
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