You got to know your A,B C. Which stations cover your area?
For Cullercoast it's (G ) for Portpatrick it's (O) for Valentia in Ireland it's (W) they all broadcast weather information roughly every 3 to 4 hours and gale warning on receipt.
Just programme your Navtex with the designated Letter for the station you require otherwise you will be swomped by transmissions from all and sundry from far and wide. There's lots of info on the web about Navtex, just Google it.
Athough I am in Ireland I believe for Niton you need to programme in B1 to get Niton's transmissions. Weather times are 0840 and 2040utc. Gale warnings on receipt. If still no messages received then check your aerial connection. Hope this helps. Russ
Sorry I may have given you a bum steer,Reeds 2007 almanac states Niton designated (E) so programme E into your set. Broadcast times 0040 0440 0840 1240 1640 2040.
cullercoats is G Portpartick is O. Good luck Russ