Whirlpool [F4E1] fault codewhat it means and how to fix it

The tech sheet calls this a cavity temperature sensor failure. The public page for the same code names a microwave sensor or thermistor, which is the same component under a more generic label, so this is one of the codes where Whirlpool’s two sources are close enough to publish jointly. A thermistor is a resistor whose resistance changes predictably with temperature, and a control board reads it by measuring that resistance. It follows that there are only three ways for the reading to be unacceptable: the resistance is far too high, which is what an open circuit looks like; far too low, which is what a short looks like; or plausible but wrong.

The first two are usually a broken wire or a chafed one, and they are what this code most often is. The third is the awkward one, because the appliance cannot tell a sensor that reads twenty degrees low from a cavity that is genuinely twenty degrees cooler. What the code does not mean is that anything is overheating. Whirlpool have a separate family for heat that is actually present — F8E4 and F8E5 for the exhaust air temperature, and F8E0 to F8E3 for an airflow restriction — so a temperature sensor code is about the instrument rather than the temperature.

In practice the appliance will often still microwave and refuse anything that needs to be controlled by temperature, because the microwave function does not depend on knowing the cavity temperature and a convection or sensor-cooking programme does. Whirlpool’s note about F4E1 has an odd afterlife elsewhere in the group, which is worth knowing if you own a Hotpoint rather than a Whirlpool: one Hotpoint UK manual singles out F4E1 by name as the exception to its generic fault row and then never explains it anywhere in the document.