Set Square wrote:

Chances are that the room in question is picking up heat from other
surrounding rooms to achieve a level 4 temperature without that particular
rad needing to be on.

If they're *all* on 4, and are *all* cold - wait a bit for the house to cool
down a bit, and they'll all come on.

Also check that you don't have the room stat set so low that it cuts off
the boiler before the rad valves get a chance.

--
Cheers,

John.

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