The temperature control of our bar mixer tap/shower became very stiff (almost unturnable) so I removed it today and free it up with a pipe wrench. Whilst it's a lot better I really want to find out exactly what caused it to seize and perhaps prevent it happening again.

The problem is, I can't seem to dismantle the cartridge any further. The cartridge is as shown he

http://www.newtonnet.co.uk/permanent...cartridge1.jpg

The circlip was removed from the position it is sitting below, and this has allowed the centra shaft to be pushed in for ~5mm. With a normal tap cartridge it would of course be possible to push it all the through but in this case I think it is what I assume to be the thermostatic element at the other end preventing this:

http://www.newtonnet.co.uk/permanent...cartridge2.jpg

With pliers I can rotate the red plastic ring ~180 degrees but it doesn't appear to be unscrewing. Before I break anything (the cartridge is working now, at least for the time being) does anyone know how to remove this ring/end, assuming that's what I need to do?