Jemp vent openers maintenance

I've been given 3 old jemp vent openers that dont appear to work at present. One is closed up completely the other two appear to be stuck wide open as though its too warm...I've tried putting them in the freezer and this changed nothing. So they have all had a spray of WD40...is there anything else I could attempt to do to get them working again?

Many thanks

Steve...

 

I've never used Jemp ones Steve but I think they mostly work on the same principle of expanding wax in a tube, dont they??

I've replaced the cylinders on my Bayliss ones once or twice over the years.

It sounds like the piston might have seized in the cylinder, or sometimes the cylinder seals go, and they leak.
Losing all the wax.