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Smart TRV failure mode. New to me, so may be to some others as well.

Radiator was getting hot when it should have been off. Valve appeared to respond to software normally, sensors seemed OK, signal OK, battery OK. Valve reported fully closed ... but the radiator got hot.

OK, I assumed, the mechanical/-plumbing bit of the valve is stuck, so I'd need to hit it (gently!) with a hammer.

But no, I could push it down by hand easily.

However the valve head felt a bit loose as I'd taken it off - eventually I worked out that the vibrations from the motor over the months had unscrewed it somewhat. Now that I've tightened it up properly it appears to behave correctly again.

See, it isn't *always* DNS.