How to drain a single radiator without draining the whole system
⚠️ After refilling, repressurise a sealed system to 1–1.5 bar via the filling loop, and dose with inhibitor if system water was significantly diluted.
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Draining a single radiator is necessary to remove it for decorating, replace a leaking valve, or remove a cold radiator. You can isolate the radiator without draining the whole system.
Turn off both valves at the radiator — the TRV (thermostatic valve, usually one side) and the lockshield valve (the capped valve on the other side). The lockshield cap unscrews or lifts off to reveal a valve stem — close it with pliers, counting the turns so you can return it to the same position later.
Open the bleed valve at the top of the radiator to break the vacuum, using the bleed key. Keep a cloth ready as some water may drip.
Unscrew the union nut on the TRV end of the radiator (anti-clockwise, with a spanner on both the nut and the valve body to avoid twisting the pipework). Water will run out — have a large container ready or attach a hose to the tail.
Tilt the radiator to drain the remaining water from the opposite end, then disconnect the lockshield union nut. Carry the radiator out (they are heavy — have help for anything above 1200mm long).
On refitting, reverse the process. Reconnect both unions hand-tight first, then tighten with a spanner (no PTFE tape needed on compression-style unions). Open the lockshield the same number of turns as before. Open the TRV. Bleed the radiator, then check for leaks at both connections.
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