On Tue, 17 Sep 2013 20:37:36 +0100 (BST), "Dave Liquorice"
wrote:

On Tue, 17 Sep 2013 18:48:32 +0100, Davidm wrote:

Are they fixable or is the only solution to renew the whole thing?

Donno about fixable but I shoul imagine you can get replacement
inserts. Bit off they have started to leak after just four years. Get
in touch with Drayton and see what they have to
say.

Anyone have a magic solution for doing this that avoids draining the
system (it's an open vented system with a header tank)?

http://www.toolstation.com/shop/Hand...s/Radiator+Val
ve+Change+Kit/d10/sd210/p31768

http://tinyurl.com/m3jhbc4

They do work, I've used them when a TRV here got stuck and I wanted
to take the insert out. Just make sure the system has no leaks and
only open it at *one* point at *any* time. There might be a little
spillage so still take precautions to protect carpets/decorations
etc.
Ah yes, I've got a couple of these, I guess I have to plug both the
feed and vent pipes at the tank. The "negative pressure" of the water
won't damage anything in the boiler will it? I've heard tales of
people who have seen hot water cylinders collapse when these plugs
have been used on the hot water side of an open vented system and then
opened a tap at the lowest point!