A5
Junkers DHW Flow Sensor / Turbine Fault

A5 displayed, no domestic hot water even when tap is opened

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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

Blocked DHW flow turbine in Junkers hydraulic block, Limescale buildup, Faulty DHW flow sensor, Wiring fault

How to Fix / Troubleshooting

Safety first: Turn off power and close cold water inlet before opening DHW components.

  • 1. Check water flow: Open a hot tap fully and verify that water flow is strong. If weak, the issue may be with the plumbing, not the furnace.
  • 2. Clean DHW filter: Many Junkers combi units have a filter on the cold water inlet. Isolate and clean this filter to remove debris.
  • 3. Inspect DHW flow turbine: Remove the DHW flow sensor/turbine assembly from the hydraulic block. Check for limescale or debris preventing rotation. Clean carefully and reassemble.
  • 4. Sensor test: With power on and water flowing, a technician can test the sensor output to the PCB. Replace the sensor if no signal is detected.
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Repair Difficulty

Medium 3/5

Required Part

DHW Flow Sensor / Turbine
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