Mixer Tap won't turn off

[SammyG]

Got a strange problem with a mixer tap.

The hot tap was stuck open and wouldn't close, I took out the tap barrel and it had seized completely. Replaced it with a new barrel and this worked ok, until I put the metal tap handle back on and then it will open but won't close again. I then have to drain the system, remove the barrel and re-install it, to stop the flow.

Anybody got any idea of anything else I can try?

 

[Burnerman]

If the spline length on the new tap insert isn't exactly the same length as the original one, then replacing the tap top could cause it to bind.
John