Radiator pinhole leak
Check the steps below first — if you\'re not confident, get it fixed safely today.
Find a Gas Safe engineer near you →⚠️ Do not use leak sealer products in your heating system — they can block the boiler heat exchanger and cause a far more expensive repair. A leaking radiator must be replaced, not patched.
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Most likely cause & what to check
A pinhole leak in the body of a radiator is caused by internal corrosion from sludge (iron oxide) — it is a permanent failure of the steel panel.
Isolate the radiator by closing both valves — TRV fully to 0, and count and note the number of turns to close the lockshield valve.
Dry the surrounding area with towels. Radiator water is dark brown-black sludge and will permanently stain carpets and flooring — put down towels and a dust sheet immediately.
Call a plumber to replace the radiator. Bring the valve measurements (centre distance between valves, and whether 15mm or 22mm tails) to help source the correct size replacement. Standard single-panel radiators cost £30–£120; labour is £80–£150/hour.
When the new radiator is fitted, consider adding central heating inhibitor to the system (Fernox F1 or Sentinel X100) to prevent future corrosion — cost £10–£20.
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