Fischer Paykel Dishwasher DD605H Panel Fuse Blown

Went to this dishwasher about a week ago. The top draw was showing error F9 control panel problem. I swapped the bottom draw control panel to the top draw and the top draw to the bottom draw. Result the top draw worked fine bottom draw F9. The customer asked me to leave the top draw working as its easier to load. I ordered a new panel OUCH and fitted the new panel to the top draw and refitted the original panel to the bottom draw thinking the customer used the top draw more often so a new one should last longer. Started both draws and all well. Four hours later the customer phones to tell me that the F9 fault is back on the top draw. I took the first failed panel to my workshop to try and fathom out what the problem is. There is a 800mA fuse that was blown, I’ve ordered a replacement from Maplins. Any ideas on what can cause this fuse to blow?