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The 5 amp low-blow fuse I just tried replacing keeps burning out. What could be causing this?

A short I would guess?

Although Endo's answer is pretty sharp, so is your problem. The short, if it is a short, may be just about anywhere.
You will ave to try to isolate the problem... I would not want to be in your shoes.

I would start by removing the top cover as well as the the face panel (just above the tray) to visually inspect for dangling wires or parts that are not in place. Most of the terminals are visible from the top. Also look for discoloured wire insulation. I cannot recall how easy it is, but I would disconnect the brew boiler heating element and turn the machine on to see if the element has shorted. If you do this, MAKE SURE you do not leave dangling wires with non insulated terminals! This of course would depend on how comfortable you are around electrical circuits.

If you have no obvious wiring issues -- or even before going through the trouble of removing the top and checking it -- I would suggest that you try swapping the fuse holder, instead of just the fuse. I was having a similar problem, and it turned out that the fuse holder -- and not the fuse itself -- was the culprit. Once the holder was replaced, the machine continued working perfectly.

It hasn't been clearly established which fuse. There are two - one under the the back left bottom corner of the chassis where the power cord comes in and another on the controller board. The one where the power cord comes should be 20A* and not 5A. The controller board is the only place with a 5A fuse.

I would definitely check the 20A* chassis fuse first since it is easy to get to.

* Note: Since you can easily switch between 15A and 20A modes, I assume all S1s ship with a 20A chassis line fuse.

Where is the one on the controller board? Do you have to take it appart to access it?

You can see the location of the 5A glass slo-blo fuse in two documents:

1) The S1VII User's Manual page 19.
2) The 2008 Firmware Upgrade Manual page 5 bottom photo. The ribbon cable, which is covered by a large black shrink wrap tube, goes right in front of the fuse but you can see the silver end of the fuse and the fuse holder just above the row of four orange relays.

The main reason to show you the firmware upgrade manual is that this manual was intended for complete removal of the board for shipment back to Chris Coffee. If you need to replace the 5A fuse, use this as a guide and go just as far as you need to in order to get to the fuse. I am sure you can access the fuse with many of the cables still connected but you will need to get the black box containing the controller board out of the chassis where you can remove the lid to access the board.

chas wrote:I would definitely check the 20A* chassis fuse first since it is easy to get to.

* Note: Since you can easily switch between 15A and 20A modes, I assume all S1s ship with a 20A chassis line fuse.

My machine stopped working, couldn't find any reference to the 20A fuse in the manual, but thankfully found it here. I'm off to the store tomorrow to pick up a new one. I wonder why it blew. Hopefully it won't repeat. Thanks for the pointer.