E4
Remeha
Flow temperature sensor fault (open or short circuit)
Display shows E4, furnace does not fire, pump may run
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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, Broken or shorted sensor wiring, Poor connection at main control PCB, Water ingress in sensor connector
How to Fix / Troubleshooting
Safety first: Isolate the appliance from the mains before accessing the electronics or sensors.
- Locate flow sensor: The flow NTC is usually clipped or screwed into the flow pipe leaving the heat exchanger. Identify the sensor and its two-core cable.
- Check connections: Ensure the sensor plug is fully seated on the sensor and on the main PCB. Look for corrosion or moisture in the connector; dry carefully if present.
- Inspect cable: Follow the cable route and check for cuts, pinches, or signs of overheating. Replace the cable if damaged.
- Resistance test: With power off, measure the NTC resistance at room temperature and compare with Remeha's chart. If the reading is open circuit or near zero ohms, replace the sensor.
- PCB check: If a known-good sensor still gives E4, the NTC input on the PCB may be defective and the main control PCB may need replacement by a technician.
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Repair Difficulty
Medium
3/5
Required Part
Flow Temperature Sensor (NTC)
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