, this counter top model would not heat but would count down the time just as if it was heating. This is an indication of a (primary in this case ) interlock switch not closing when the door is shut. Removed the panel and pulled the switch off the mount and found the switch had melted preventing the contacts from actuating. Replaced the switch with one from my stock (easier than getting a part from Sharp) and now the microwave works. Just a note about interlock switches, the primary and secondary are N.O. while the monitor is N.C. so make sure you have the correct one from your collection before you install it. Or have extra fuses handy.