I have a different brand of boiler but do the same, it's not used during the summer except on the odd very cold day in our so called 'summer', I turned in on about two weeks ago for a few hours as it was very cold. Doing that for past 20 yrs without any issues.
I also use the immersion for hot water, the gas may be cheaper but if I want a little hot water to wash dishes in 10 mins then immersion is more practical than turning on gas and waiting until tank heats.
(Actually just wonder what exactly you mean by turning if off? I just leave mine alone, I don't turn on or off anything, the thermostat is turned down very low which means it just doesn't come on with the timer as it would in winter when the thermostat is set higher)