Originally Posted by jhlst
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Also when I press down on the valve, even quite lighty, is just sink back into the wheel and I have to pull it out again!!!
Put your thumb on the outside of the tire behind the valve stem and press hard to prevent that.
If it is a Shrader valve, and the pump won't lock to it, see if there is a tightening ring around the pump head, that will compress the rubber ring inside the pump head to make it tighter.