[eeedelli]

Thanks Ian.

Unfortunately, similar problems with hips, knees and metatarsals (an alternative to the old wartime song of hands, knees and bumpsadaisy?) means I can't stay on my feet or walk around for too long these days either. <sigh>

Anyway, although I have yet to investigate, your excellent description makes me suspect that whoever last fiddled with it (perhaps to replace the valve) might not have replaced the clip. That would allow the outer to travel with the movement of the inner, thus reducing the *effective* movement of the valve's arm to a large extent, resulting in the situation whereby the heat output goes from 'not very much' to 'not much more'!