How do I add water to a Vokera central heating boiler?

There is no water in my Vokera boiler, an engineer yesterday told me that it was installed wrong and there should be a pipe from the attic connected to it to ensure constant water. It has worked for 5 yrs with the same amount of water I assume that it has just evaporated over time. There is a pipe outside which the engineer attached a hose to in order to fill it again but it seemed that no water was going in, he now wants to do the work to connect this pipe and I am not sure if it is necessary, is anyone familiar with this and can offer advice as to how to get the water in to the system via the pipe outside with out doing all that work to permanently connect a pipe to it?