Gas water heater

The water heater shut down on gas 3 times this weekend, first time ever. Any ideas please to the most common reasons and cures would be welcome.

Abit more info on the type of system you have in your van would help with any diagnosis coming from within the forum.   
Boaby

The Truma heater will run briefly and then shut down if the winter cover is still in place. Or,
if you have a window above the Truma exhaust, there will be a switch which opens if the window is open, even slightly. This is not a "shut down" symptom. It will not allow the heater to start.   Keith

(assuming same set up) This problem was discussed a few years ago in relation to similar vans. Peter gave us a part number for a short flue extension which did the trick and only too a couple of minutes to fit.

Thanks.  The heater did not have  the travel cover fitted and lit first time as usual. I went to run hot water about 30 mins. later and it was "just warm". red light was shownig. Switched on again and this time all ok.   It did the same thing this weekend. I was wondering if it could be a spiders web in the flue or just wind direction.

Thanks for suggestions.  All working ok now. Possibly right about spider taking up residence so repeated re-lighting either burned him up or carbon mon. got him.