My Valliant turbomax boiler keeps displaying a fault code of F.62? I have read through the manuals but cannot find what this error code means. I had the boiler installed about 8 years ago. This problem has been going on for approx a week. I keep resetting the boiler. It will work again for anything up to a day but then goes back to this fault code. Will I need to call out an engineer or can I fix it myself?