Thats not enough, I'm afraid - a small volume of water will still pass.
You need to remove the TRV head completely, and replace it with a 'decorators cap' that would have come with the TRV when it was new....this effectively presses down the valve pip enough to completely close it.
John
Count yourself lucky. Turning the TRV to O will often stop water flow, only to open at night or during the day when you are out due to a temperature drop.
If you don't have a decorators cap, fit a stop end.
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