[rwg200]

Rob,
Don't know the maker of the switch.

"mine appears to be a bit sticky!"

I'm assuming that you have the round silver metal door button.  I would try a little silicone spray after depressing the button.

yes it is the round silver metal button, Sticky may not be the right explanation.....it appears to depress properly but does not operate the door, 10 or so fast presses will get it to operate.
But i will be going for the silicone spray for the first option!
thank for the advise 
allt he best
Rob