can anyone help we have just bought our caravan its an abbey spectrum520 a 1997 we have a problem with the blow air system when trying to run it on electric only it makes a terrible screeching sound after about 2mins after switch on .we can't use the gas space heating as there is a problem with a yellow flame and we been told its dangerous. but could still use the electric blow air fan heating .it does say any way in the hand book that came with van that you use one or other not both .so we opted for blow air fan until we can get fire looked at .its a carver3600stc by the way. what are we doing wrong??any advice be very much appreciated