Yes, it may be a problem if it is a very old cylinder 25 years +. Even then it's only a possibility . The worst thing that could happen is the coil could develop a pin hole leak ,and you will need a new cylinder. The fact is no one can tell for sure one way or the other.
It's an old floor standing boiler for a wall hung one. And can't get 3meters from the top of the boiler to water level in header tank. And can't raise the header. So a strong likely hood it may pump over.