vaillant ecotec plus 630 r1?

my boiler seams to have caught fire or experiance extreme heat internally. all the black plastic air pipes in front of the heat exchange have melted or caught fire. it started by the system showing a fault. f28 and f29. the system had 0 bar pressure. so i filled the sytem to 1bar. but still had the same problem. so i opened the boiler cover and found that upper part of the boiler was burnt and there is alot of carbon deposit. i dont know what could have caused this, please help me find the cause and i also dont know if other parts of the boiler are damaged due to the high heat present.