2008 Renault Laguna won't start

It's an intermittent problem that only seems to happen in the summer. It just decides not to start. I've had the smell of fuel before but last time not. No codes come up on the dash. My mechanic has had it in the past and no joy. Just seems to clear itself. It broke down yesterday and had to call out green flag. Same again no codes. Until he hooked up his volt meter on the battery. Something clicked in the engine bay and it started. Personally I'm thinking fuel pressure regulator . Thoughts please guys. Kind regards in advance.