F42
Protherm
Return Temperature Sensor Fault
F42 error: return temperature sensor readings are implausible.
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Possible Causes
Defective return NTC sensor, loose or corroded connector, sensor not in proper contact with return pipe, cable damage.
How to Fix / Troubleshooting
Safety first: Turn off power and let the system cool.
- Locate return NTC: Find the sensor on the return pipe or heat exchanger.
- Check contact: Ensure it is firmly clipped and in good thermal contact.
- Test resistance: Measure sensor resistance and compare with Protherm's chart. Replace if out of range.
- Inspect cable: Repair or replace damaged wiring.
Warning: Do not bypass the sensor; it is part of the safety and control system.
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Repair Difficulty
Easy
2/5
Required Part
Return NTC Temperature Sensor
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