Radiator always hot even when heating is off
Check the steps below first — if you're not confident, get it fixed safely today.
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Most likely cause & what to check
Check if all radiators are hot or just one — if all radiators are hot when they shouldn't be, this is usually a zone valve or programmer fault.
If just one radiator: the TRV head is stuck open or missing. Check the valve pin as described in the TRV guide. If the pin is stuck up, the valve will stay open and pass hot water even when closed.
If all radiators are hot: the mid-position or zone valve on your heating system may have failed in the open position — this allows hot water to circulate constantly. A Gas Safe engineer should replace it.
Gravity circulation is another cause on older systems — without a pump and with poor system design, hot water can circulate by convection. A plumber can fit a motorised valve to prevent this.
In the short term, you can close the lockshield valve on the always-hot radiator manually to stop circulation through it.
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Frequently asked questions
Is it harmful for a radiator to stay on when the heating is off?
It wastes energy and increases your gas bill. It also puts unnecessary wear on the boiler pump.