Leaking Radiator or Valve: Stop the Damage First
Radiator leaks tend to start small — a damp patch on a valve nut, a rusty ring on a carpet — and stay small for weeks before they get worse quickly.
Radiator leaks tend to start small — a damp patch on a valve nut, a rusty ring on a carpet — and stay small for weeks before they get worse quickly. Because the water is inhibited and often black with magnetite, it stains permanently, so isolating it early matters as much as the repair itself.
Work out where it's leaking from
Dry everything thoroughly, wrap tissue around the valve nut, the gland below the head and the pipe joint, and see which one is wet after an hour. A leak at the spindle is a gland packing issue; at the nut it's a compression joint; from the panel itself it's corrosion and the radiator needs replacing.
Isolating without draining the system
Most radiators can be isolated at the thermostatic valve and the lockshield, then removed and dealt with without draining the whole system. That keeps the rest of the heating working and avoids introducing a system full of fresh water — which, as with pressure loss, brings its own corrosion problems.
Valve replacement and TRVs
If we're replacing a valve, it is usually worth fitting a thermostatic valve where there isn't one, so the room can be controlled independently. We check which valve is the lockshield and re-balance the system afterwards so flow isn't thrown out across the rest of the house.
When a radiator is beyond repair
Pinholes are corrosion through the panel from the inside, and sealing them is a temporary measure at best. Replacing the radiator and addressing the water quality that caused it — inhibitor, magnetic filter, and a clean if the system is dirty — is the durable fix.
Common questions
Can a leaking radiator be repaired or does it need replacing?
Valve, nut and gland leaks are all repairable. A leak from the panel itself is internal corrosion and the radiator should be replaced — patching it rarely lasts.
Why is the water from my radiator black?
That's magnetite — iron oxide from internal corrosion. It means inhibitor has been depleted and the system would benefit from cleaning and a magnetic filter alongside the leak repair.
Can you replace a radiator with a different size or a towel rail?
Yes, provided the heat output still suits the room. We calculate the required output rather than matching by physical size, since modern radiators produce different outputs for the same dimensions.
Do you re-balance the system afterwards?
Yes. Changing a valve or radiator alters flow distribution, so balancing afterwards keeps every room heating at the right rate rather than starving the far end of the circuit.