I'm going to add a valve so I can turn it off in hot weather as a bit of the hot air always finds it's way past the flap even in the off position.
I've been through a couple of these valves, and found that they all tend to leak hot water (through the valve), leading to the heater being permanently on.
Please see
this topic, where I fit an
electrically operated ball valve, that blissfully is leak free, and was good for the summer.
I'd recommend it over the originally fitted cable operated valves.
