Microwave makes loud bussing noise and does not re-heat- I placed some popcorn to try-it read sensor error–I called a repairman–It will be until sometime next week 
Any advice I also did refer to the manual- no luck
Most likely the problem is a bad magnetron. The microwave has to be removed from the cabinet to access the part. If you need the part numbers then post the complete model number of the microwave. "XL1800" is not a valid model number.
Gene.