Heater Valve Doesn't Close?

[Bob Fabie <rmf3860@erols.com>]

During my recent rebuild, I replaced the heater valve on my TR6 (the
thing that sticks up from the head). The cable is also new. The valve
appears to be operating in that it slides all the way to the top and all
the way back to the bottom. However, it's obvious that the valve is not
closing since the heater hose is hot and there's hot air in the
passenger compartment.

Can anyone help with any information. Could the valve be going through
its motions but the valve actually not closing?

Thanks

Bob Fabie
'75 TR6
(now with 156 miles on the new engine)