Hello jason

Flushing it out sounds the best bet tbh....... Like what has all ready been said, if it is orange water then it will be pumping over so could be a blockage.....

Flush it out, then refill but leave a hose pipe connected to a drain point, this will constantly flush the system. Then put some inhibator into it and go from there...

By any chance, it isnt a Potterton Suprima Boiler is it????????.....It is just that they do exactly what you are saying when the PCB board fucks up on them.

Hope that helps

Mark