non cooperative radiator nut


We have small two storey terraced house in north London and the gas fired central heating radiator started leaking in the first floor bedroom at the tap. When it was opened up a bit the other day.
The nut on the top (not the two flat sided tap spindle) will not take a 13 mm spanner and the 14mm spanner slips around. Is there a special size spanner I should buy, or do I have to go to town with the stilson?
Being a complete novice, I'm not sure what my next move should be...try to tighten it? or undo it and replace. If so where should I be turning off the water? If I turn off the water and then undo it, am I likely to get much of a sudden flood? Any advice to a complete beginner much appreciated, thanks.
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17/32 inch?

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A large adjustable wrench might do the trick. I believe the nut you refer to is the packing nut through which the valve stem passes. The packing may swell enough on it's own to seal or you may have to tighten it or have to remove the nut and add some packing. As for a flood, secure the water supply to the system as most are pressurized to 15lbs or so. You should be able to do the job on one good sized towell. JWBH wrote:

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Try an adjustable spanner, but buy a good one not some cheap far east rubbish. Best buy is Bacco, expensive but nearly as good as a "proper" spanner.

If you crank down the valve you'll "probably be ok" but if it all goes Pete Tong, you'll get all the water in the central heating system above the point at which you cause the leak. If it was me, I'd try tightening it up but failing that I'd drain down the system, and replace the whole valve. Use a thermostatic if there isn't one there already.
A plumber will charge you silly money for a relatively simple procedure.
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Sounds like a job for a good old-fashioned 1/4" Whitworth spanner.
Steve
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