Here we use a temperature sensor mounted towards the top of the boiler
, the electrical signal from the sensor is then fed back to the machines control circuit which then supplies either a DC or an AC feed to operate a solid state relay that supplies the power going to the element
The operating principles are in line with the diaphragm system above, but due to full electronic control we have a much tighter control of when power is supplied to the element and generally longer life for the element due to power only being supplied when the mains supply is at its zero point in the phase.
For: Accurate heat control, no moving parts, reduced running cost.
Against: Greater skill level in fault finding