I have tried many of the methods stated here about how to fix my wifes steam generator. Cleaned the pipes to and from the boiler, ran thru vinegar solution, changed the thermal switches under the boiler and even took the boiler apart to clean any scale. I do not advise taking apart the boiler tho as 7 of the eight bolts sheared off and had to be drilled out (such is the problem with threading steel into aluminium). my symptoms were as follows:-
1: after switching on the iron it would heat up, flashing red light would turn green.
2: click the steam button and some steam would come out of the iron then stop, the green light would change to flashing red again and a beeping sound if the button was pressed again
3: the iron would not heat up again then go into standby
Underneath the boiler there is a thermistor screwed to it.
A thermistor is a resistor that changes value with temperature. as the temperature increases the resistance decreases
After taking a few measurements i noticed that the resistance when the boiler reaches 100 degrees C is around 3kOhms. This helped me determine the value of the thermistor at 25 degrees C (as this is how they are graded)
As the boiler hits this temperature the relay that controls the power to the boilers heating element drops out and it starts to cool. Cooling is accelerated by clicking the steam button which runs the pump. When the temperature drops below a set level the relay should kick in to put power back on to the heating element. This was not happening in my case so instead i used a 47kOhm resistor in place of the thermistor and the heater relay kicked in.
It appears that the thermistor was not working as it should do. As the temperature started to drop the resistance was not increasing enough to tell the control circuit to put the power back on to the heater relay.
The thermistor was replaced for one of a similar value and this has now cured the fault.
NOTE: The thermistor fitted has two leads, one at either end. I struggled to find one of this type so i substituted it with a 'bead' type that has both leads at one end.This means the bracket that holds the thermistor needs to be altered slightly.
Hope this helps
Tony
October 2011