Is this an RC filter?
All of the answers so far seem to be assuming that the pin on the microprocessor is an ADC input. If that's how you're planning to proceed, that's fine.

However, your original question is about the components in the original circuit. In my experience, "white goods" (household appliances) use the absolute cheapest control circuit implementations they can get away with, and I think it's likely that the micro they chose doesn't have a hardware ADC.

There are ways to measure an analog value using just a comparator, or even just using the threshold voltage of an ordinary digital input pin. The software alternately drives the pin low for a variable amount of time, and switches the pin to input mode and checks to see whether the voltage has crossed the threshold. You can infer the analog value from the width and/or the number of pulses required to keep the input near the switching threshold.

This method could easily account for all the components you see. For example, R3 could serve to limit the current into the pin when it is driven low.