Although you are unlikely to need heating during the summer months, it is always suggested that if you intend to shut off your boiler for an extended time, you should switch it on often to avoid the internal workings from seizing to lack of usage.
It just has to be turned on for a few weeks. It doesn't take much work, but when you consider the alternative - a boiler that fails the first time you use it in the fall – it's likely to save you a lot of frustration and money.