Vaillant Gas boiler fault S.93
Flue gas measurement not possible
Gas boilerWhat it means
Flue gas analysis is not currently possible.
Likely causes
- Leak in flue system
- Flue gas recirculation in extended flue gas installations
- Incorrect flue fall causing condensate to not drain back to boiler
- Condensate pooling in flue leading to blockage or corrosion
- Use of mineral-oil-based grease on flue pipe seals causing seal damage
- Air/flue pipe not completely installed
- Front casing not installed/closed
- Empty condensate trap / siphon allowing flue gas into room air
- Damaged seals due to use of grease instead of water/soft soap during installation
Where to start
- Check the flue gas installation is intact in accordance with the latest gas safe technical bulletin and installation instructions
- For extended flue gas installations, check for flue gas recirculation using the air analysis point
- Use a flue gas analyser
The full answer, free
- 9 more checks in order
- The readings and component tests from the manual
- How to put it right, step by step
- The manual page for this fault (page 59), 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 Gas boiler. Check the model on the data plate before you order parts.
Other Vaillant Gas boiler 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
- F.85Flow and return temperature sensors installed incorrectly (inverted)
- P.02Minimum load check programme
- S.42Flue non-return flap closed