ATAG Domestic Hot Water (DHW) Temperature Sensor Fault

Furnace displays F3, often with erratic or implausible temperature readings

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

Possible Causes

Defective DHW NTC sensor, Loose or corroded sensor connector, Sensor not in full contact with DHW pipe or heat exchanger

Safety first: Turn off power and allow hot water components to cool.

Locate the DHW temperature sensor on the plate heat exchanger or DHW outlet pipe.
Check that the sensor is firmly clipped or inserted into its pocket.
Unplug and reseat the sensor connector on the harness and PCB.
Inspect the cable for damage.
If available, measure sensor resistance and compare with ATAG's NTC chart; replace if out of range.
After replacement, restore power and reset the unit to clear F3.

Medium 3/5

ATAG DHW NTC sensor

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