Sorry to come into this so late, I would like to give you an explanation as to how an electrode boiler works.
Simply, water out of the tap (faucet), has "impurities" in it, that is not to say the water is impure, what I'm talking about is the trace elements that could be in the water, it could be cobalt, magnesium, calcium, you name it, but they are there, but this chemical make-up, affects the electrical resistance of the water in the electrode boiler, this is used to great effect.
As you said above, you had a boiler that tried to heat de-ionised water, that for a start is not going to work that well.
The reason behind that, is because pure water does not conduct electricity and to be fair this sort of water is bad for our health, if it is drank on a regular basis.
But, the electrode boiler has 3 live probes inside the heating chamber, at different heights, normally 50mm between them, there is a temperature probe below the electrodes, this starts and stops the heating via a relay or contactor.
Normally, there is also a "run dry" switch at the bottom of the chamber that turns off the power to the electrodes should the chamber have no water.
Effectively what happens, when the chamber is full, the heating process starts, current flows through all of the probes, the water is boiled pretty much instantly through electrical resistance through the water.
Not long after I finished my time as an Electrician, I got sent to a factory, that used a large electrode boiler that used 400V, to create steam for the presses (it was a clothing factory, when we had them here), I was scared by the size of the thing, the tank was massive and someone had mucked around with the tank pressure switch, I walked back to my van to get my Duspol tester and the tank split down the side, that bought the whole factory to a halt.