Locks for radiator valves

My gran has thermostatic valves fitted to her radiators. I seem to remember you could get "locks" for these to prevent them being turned up too high or down too low. Does any one have any experience of these locks or an addy to a website were these locks are for sale, can I fit "locks" to the existing valves or do I have to replace all the valves with "lockable" ones?
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Yours S.
addy not usable (not that you would try it)
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It may already be a feature of the valve. The ones on my system have moveable pins to restrict the operating range.
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Alan
mailto:news2me_a snipped-for-privacy@amacleod.clara.co.uk
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Many valves have the locks built in. You remove the head from the valve body (there is usually a big nut to undo). Under the head are lots of holes, one per degree C. You take the locking pin from the parking position (i.e. 30C) and put it where you want it. Make sure the valve is set to 0C before you insert the pin. Then reattach to the valve body.
Christian.
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