This fault according to Vaillant Instructions and Servicing manual is a Heating Flow NTC Thermistor Fault or Heating Flow NTC short circuit
Cause of F23
- Inadequate Pump Operation
- Blockage Or Air Lock Within The Appliance (No Water Movement)
- Blockage Or Air Lock In The Heating System (No Water Movement)
- Check Domestic Hot Water Heat Exchanger and Domestic Hot Water Heat Exchanger Filter For Debris If Fault Occurs On Hot Water Mode Only
- Check Resistance On The Heating Flow & Return NTC Thermistors To Ensure Accurate Temperature Monitoring (Should Read 12K ohms @ 20C
Solutions to repair this fault
Check the Flow and return NTC sensors. Check the wiring using a continuity tester and resistance tester if necessary. Replace NTC, harness or PCB as necessary dependent on checks.
Make sure there are no blockages in the pipework. If there is debris in the system, flushing may be required. Then individual components may require cleaning or replacing dependent on damage caused by debris. You may need to activate the pump purge program (see P Codes). Also check the domestic heat exchanger is free of debris, cleaning the filter as necessary.
Models applicable to:
Ecotec Pro, Ecotec Plus, Ecotec Exclusive.