A8
Junkers
Primary Flow Temperature Sensor Fault / Overtemperature
Heater locks out with A8; may occur after long operation at high temperature.
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Safety Warning
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.
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Possible Causes
Defective flow NTC sensor, Poor circulation through heat exchanger, Limescale buildup in heat exchanger, Stuck or closed service valves on inlet/outlet
How to Fix / Troubleshooting
Safety: Allow the heater to cool before touching any pipes or internal parts.
- Check water flow: Open several hot water taps and verify strong flow. Weak flow can cause overheating. Clean or replace inlet filters and aerators on taps.
- Inspect isolation valves: Confirm the cold water inlet and hot outlet service valves at the heater are fully open.
- Check NTC wiring: Locate the primary flow NTC on the flow pipe or heat exchanger. Ensure its connector is firmly attached and wires are intact.
- Descale heat exchanger (if experienced): If your area has hard water and the unit is several years old, the primary heat exchanger may be scaled. A professional descaling with a pump and approved descaler is recommended.
- Reset and monitor: Reset the unit and observe operation. If A8 recurs frequently, schedule service to test the NTC and circulation.
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Repair Difficulty
Hard
4/5
Required Part
Flow Temperature NTC Sensor
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