i have a bosch steam generator, sensixx B25. how can I fix it?

had it for some years. always put filtered water in it. It has now stopped steaming after i use it for 20 minutes or so. sometimes i can iron for longer. to get it to steam again i have to turn it off for quite a while and then turn it back on again it starts steaming again. what could be the problem and could i fix it with your help?