Having managed to send two sous-vide circulators to the great electronics graveyard in the sky, I am determined not to repeat the same mistake with my third and most recent acquisition (a Buffalo DM868). The previous circulator (a German unit) had only been used 25 times over 12 months, but despite rigourously following the manufacturers instructions (i.e. not to submerge in water etc.) they both failed suddenly mid-cook. Upon closer inspection of the latest casualty it seems that water vapour had managed to collect inside the electronics either during operation or afterwards. The former seems impossible to avoid as there will always be a certain amount of condensation present during sous-vide cooking, even if a lid or insulating spheres is used with the water bath.
To check this theory, after my last sous-vide session with the Buffalo I left the circulator to vertically air dry in the empty water bath for 24 hours. Upon checking the next day, there was still considerable condensation and water droplets inside the "wet" area that houses the pump and heater components etc. In theory, if I had immediately stored the device horizontally at this point as normal, moisture could easily have seeped into the electronics. My current temporary solution is to store it vertically in the original box, but this is not a practical long-term fix as any moisture will affect the cardboard and only delay the inevatible.
In an ideal world, I'd keep it horizontally in the large plastic storage box I use to hold all my sous-vide kit. This doesn't seem like a good idea unless the curculator is completely bone dry after use, not a simple matter as the only way to reach all the nooks and crannies would be to take the guard off and dry with a hairdryer or similar after each use.
So how to others dry and store their circulator after use? With hindsight, it would have been more cost-effective to save up and buy a proper temperature controlled water bath as this seems to be an inherent design flaw of many stick design circulators.