Hope I fixed it, heres the pic.
Pretty much fell out of the hole (green plug as seen in pic) and after taking the bottom out of the heater blower, which was full of water - realised I could put my hand right up the vent and to the plug hole. So I cleaned up the hole and green plug, glued it in with guttering silicon and see how it goes. Noticed there was a foam piece under the black cover (can see a shiny bit to the right of green plug) it was wet too so I took it off, hope this wasnt a bad idea??
Thanks for all your help.