Eberspacher D2 wont work on hookup,fine on battery

We have a 2003 Autosleeper ES symbol, bought this year from a dealer who put in a new heater. We do not understand and the dealer does not seem to either why the heater will work fine from the leisure battery but as soon as we connect van to hookup on site or at home it will start to rev up but does not ignite , it just blows cold air and after a couple of minutes it stops. This does not seem logical and all the other electrics are fine. Off to the dealer again but I am suspicious that they don't actually check it connected up as they just say it's fine and must have been the weather. We have checked it ourselves many times. I think I will have to stand over them and insist they connect it up. Also any idea why our hookup cable is white and everyone elses is orange,came with van? Thanks to any clever folk out there. Carolyn