Pilot light wont stay on on boiler?

i have a saunier duval thelia 23 which the pilot wont stay on this morning. was ok last night. i suspect a thermocouple has gone down. this i have had before on older type boilers.. can see the thermocouple at the pilot end. difficult getting to other end but will persevere if others think this may be it.. pilot lights. i let go after 20-30 secs but goes out. what do you think. ??