This document is based on my experiences with a Bosch 800 series dishwasher, built in 2015. It probably has wide applicability to other models of Bosch dishwashers over many years.

The E27 error code has a cause listed as "mains voltage too low". The user manual says "Not an appliance fault, have the mains voltage and electrical installation checked." As usual with Bosch, the cause was incorrect, and the suggested remedial actions are useless.

It turns out that the problem in my case (and I suspect most cases of E27 errors) was due to a fault with the control board (so much for "not an appliance fault"). My particular board was labelled EPG70011 9000889767 and was manufactured on 19 Nov 2014. A replacement board costs AUD$350 and was out of stock. Fortunately, careful inspection of the board revealed the issue: two vias on the PCB were corroded to the point where they no longer made contact across the board, see the image of one via below:

The via in question is the one to the right of the 103 resistor. It can be fixed by cleaning the board with isopropyl alcohol, inserting a strand of copper wire, and soldering it to the tracks on either side. I followed up with cleaning the board again to remove the solder flux, and then conformally coating the board to stop further corrosion, and baking overnight in an oven to harden the coating.

This is just poor design by Bosch and cheap manufacturing. The vias in question were tiny and ripe for corrosion over a period of years. They could have been made larger, with heavier copper, even gold coating, followed by conformal coating. For a close to top-of-the-line dishwasher, you would expect such attention to detail.

It is likely that the vias were related to sensing the DC voltage on the output of the switch mode power supply. The firmware should be able to recognise an open circuit on the sense line, and then try spinning a motor and checking the current to see if the DC voltage is actually OK. As it is, the firmware seems to keep checking the sense line for 15 minutes to over an hour (depending on the washing cycle selected) before eventually giving up and declaring an E27 error.

I'm sure that Bosch is aware of this problem, but they don't provide any guidance on-line as to how to resolve it. I for one won't be buying another Bosch dishwasher, and I will give such advice to anyone who asks.