easy,unscrew trv tail in radiator,special tool may be req.
get a half inch black iron cap from your local heating supplier,
apply ptfe tape to thread on trv tail and screw cap onto it ,then fit back onto valve.
yes and some trvs have a positive stop and need no cap,but to be 100% sure,i would cap off as i advised.
yes i went to an insurance claim where a child undid the plastic cap on a drayton valve resulting in a scalding incident not to mention lots of property damage.
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