While on a recent trip to Michigan we needed some heat so we flipped on the Aqua-Hot furnace in our '07 Travel Supreme. When no heat was produced we checked outside and found the fan on and diesel fuel leaking out of the exhaust pipe. After checking with Aqua-Hot service department we were told that it was most likely the flame sensor not functioning so we had our technician replace it and it seems to be working fine now. Fortunately it was not the $900.00 control box. We could not find this particular problem listed in the 118 page service manual trouble shooting section, but the technician, Matt, at Aqua-Hot was very helpful and was correct with his diagnosis. Just wanted to see if anyone else has had this problem and maybe this information can be helpful to someone else. Thanks!