Just fixed mine - hurrah!
Symptoms were gradually becoming more unreliable in heating water, i.e. cold and wet after wash.
Took advice from this site - I'm repeating the main solution I received but adding more detail to get to the problem areas.
Removed right hand side (from front), after unplugging of course.
(Need to remove lid - two screws at back and slides back and lifts, Remove front bottom panel - Drop door to bottom and crawl underneath and remove two inset screws, Remove side - obvious screws, 4 or 5 off)
Checked heater unit continuity (behind pump in base). Unplug two wire plug to heater and checked continuity on terminals in connector of heater - mine was approx 25 ohms). I'm guessing if open-circuit then heater is faulty.
As this looked ok I then removed both front panels - lots of screws from the inside of the door - You might only need to remove the top front panel but I removed both to give easier access to the controller panel - longer free cable lengths meant more easier access.
In the top panel (the switch panel), unclipped (4 clips) the main controller box (on right-hand side). The controller is hinged, pry open slightly while unclipping a further 4 clips. Carefully open controller - it has a delicate fexi-cable connecting two boards. Unplug 6 off connectors to free it from front panel. These are awkward as they are captive but the plastic holding each connector can be gently pried clear to remove each, (make a diagram of where they go before removal!)
I removed both boards by prying them out from more plastic retaining lugs but you only really need to remove the "connector board". I removed both boards to avoid excessive strain on the flexi. Turning over the "connector board" showed the track which goes to the thickest Orange wire from the controller - which I think feeds the heater, this was discoloured. This connection was from beneath the large black relay. I re-soldered this terminal connection and added a thicker wire along the thinnest part of the track. After re-assembly the dishwasher now appears to work reliably. I am not a genuine repairer just a fairly reasonable DIY'er who hates to throw things out due to minor faults.
Hope this is of use.
Rob S
September 2008