Worcester Bosch [E2 222] fault codewhat it means and how to fix it

E2 is a flow temperature sensor fault, with 222 as the sub-code Worcester use for the flow temperature condition. The flow sensor reports the temperature of water leaving the heat exchanger, and virtually every operating decision the appliance makes depends on it — how hard to fire, when to modulate down, when to stop. When that reading becomes implausible, whether open circuit, short circuit, or simply a value outside anything physically sensible, the appliance shuts down rather than operating blind.

Two quite different situations produce this. The more common is that the sensor or its wiring has failed, in which case the water temperature is perfectly normal and only the measurement is wrong. The less common is that the temperature genuinely is extreme because circulation has stopped, in which case the sensor is working correctly and telling you something important. Those need entirely different repairs, which is why an engineer measures the sensor resistance rather than simply replacing it.