Hi, I have an oil boiler and the fan assemly that blows the oil into the boiler seems to be jammed. We had a period of low voltage and hat burned out the control box and the boiler fuse went. Fuse also replaced. Now when switched on the boiler hisses for a moment or two the makes a funny noise and locks out. The fan in the "squirrel cage" seems to be solid and won't turn at all. Should it be like this or has it jammed