Vaillant VU 446/5-5 / VU 606/5-5 fault F.85
Flow and return temperature sensors installed incorrectly (inverted)
Gas boilerWhat it means
Fault indicating the flow and return NTC sensors have been swapped or installed on the same/incorrect pipe.
Likely causes
- Flow/return NTC installed on the same/incorrect pipe
- Defective heating flow or return temperature sensor
Where to start
- Check that the flow and return NTCs have been installed on the correct pipe.
- Pull out the heating flow (4) and return temperature sensor (3)
- Remove the heating flow (1) and return plug (2)
The full answer, free
- How to put it right, step by step
- The manual page for this fault (page 63), right under the answer
Safety: Isolate gas and power before you open the case. If you have been into the gas side, do a tightness test, and a combustion and flue check before you hand back. Gas Safe (UK) or RGI (Ireland) work only.
From the Vaillant manual for the VU 446/5-5 / VU 606/5-5. Check the model on the data plate before you order parts.
Other Vaillant VU 446/5-5 / VU 606/5-5 fault codes
- F.00Flow temperature sensor interruption
- F.01Return temperature sensor interruption
- F.03Cylinder temperature sensor interruption
- F.10Flow temperature sensor short circuit
- F.11Return temperature sensor short circuit
- F.13Cylinder temperature sensor short circuit
- F.22Safety shutdown: water deficiency
- F.23Safety shutdown: temperature spread too great
- F.24Safety shutdown: temperature rise too fast
- F.25Safety shutdown: flue gas temperature too high
- F.27Safety shutdown: flame simulation
- F.32Fan fault
- F.33Air pressure switch fault
- F.64Fault: electronics/NTC
- F.65Electronics temperature fault
- F.72Flow and/or return temperature sensor fault
- F.74Water pressure sensor signal outside correct range (too high)
- F.75Pump fault/water deficiency
- F.77Accessory fault (flue non-return flap, condensate pump, etc.)
- F.83Flow and/or return temperature sensor temperature change fault
- F.84Temperature difference fault at the flow and return temperature sensors
- P.02Minimum load check programme
- S.42Flue non-return flap closed
- S.46Comfort protection: minimum load, loss of flame