On Sat, 2 Nov 2013 14:51:32 -0000, "Phil L"
wrote:

that said, the can of foam is never removed from the gun until it's
completely empty, this is where your problem may be, the set foam could be
in the top of the can rather than the actual gun, although this doesn't
explain why the cleaner won't come through

Yesterday I picked up the foam gun and the dregs of the last can on it
squirted out fine, even though it was well over a year since it was
last used. Same as you, the valve screwed down and left.