How to drain a hot water cylinder
Check the steps below first — if you\'re not confident, get it fixed safely today.
Find a Gas Safe engineer near you →⚠️ Never drain an unvented (pressurised) cylinder yourself — it requires a G3 qualified engineer. For vented cylinders, always let the water cool first.
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First, identify your cylinder type. An unvented cylinder has a pressure relief valve (a small pipe running to an outside drain) and is fed directly from the mains — do not drain this yourself.
If you have a vented cylinder (fed from a cold water tank in the loft), turn off the boiler and immersion heater and wait for the water to fully cool before doing anything.
Draining a cylinder involves attaching a hosepipe to a drain-off cock and opening it — it's straightforward but fiddly in an airing cupboard. If you're not confident, call a plumber rather than risk flooding.
Find a Gas Safe registered engineer near you and get it fixed properly.
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