BoilerFaultCodesWhat the manual says
Manufacturer manualUnstable flame signal error air in gas
From this model's manual
Verified against the Vaillant/Vaillant Ecotec Pro Ecotec Plus Regular installation & service manual.
What causes this fault?
This fault occurs when the boiler's control system detects that the flame is flickering or unstable, making it unsafe to continue operating. The most common reasons are air bubbles trapped in the gas pipework after a service or a buildup of carbon on the sensing probe that prevents it from 'seeing' the flame correctly.
Engineer required
This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Related fault codes
All 101 fault codes on the ecoTEC Pro / ecoTEC Plus
Seeing a different code? Every code this model can display, in one place.
F.00F.01F.02F.03F.10F.11F.12F.13F.20F.22F.23F.24F.25F.26F.27F.28F.29F.32F.42F.49F.52F.53F.54F.55F.56F.57F.61F.62F.63F.64F.65F.67F.70F.71F.72F.73F.74F.75F.77F.78F.80F.81F.82F.83F.84F.85F.90F.91F.92F.93F.94S.00S.01S.02S.03S.04S.05S.06S.07S.08S.10S.11S.13S.14S.15S.16S.17S.20S.21S.22S.23S.24S.25S.26S.27S.28S.30S.31S.32S.34S.39S.40S.41S.42S.46S.53S.54S.57S.58S.61S.62S.63S.76S.88S.92S.93S.96S.97S.98S.99