Mercedes sprinter non start intermittent fault

[Dsaunders17]

Hi guys. I've got an 09 sprinter which randomly won't start when I turn the key, the only warning light I get is the red temperature symbol which won't even let me crank the van, but then I just take key out and then all lights go out and she starts a dream. It's such a weird intermittent fault as it does in morning/day or night.. Anyone else have this issue before. I've spoke to Mercedes and they have never heard such thing on a sprinter. Really don't wanna take it to them as they will just scratch there head whilst charging £100's... Feel I got a better chance on these forums. Cheers, dave