BoilerFaultCodes F.00
Fault: Flow temperature sensor - NTC plug not plugged in or has come loose, multiple plug on the PCB not plugged in correctly, interruption in cable harness, NTC sensor defective
Vaillant Home Regular 12 Fault codes & diagnostics
33 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.
Regular Natural Gas 2015-2018 Discontinued
GC Number 41-044-88
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Severity at a glance
Each cell = one fault code. Hover to identify. 33 Unrated
Just want the most common Vaillant Home Regular 12 faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes
All 33 documented codes
Tap any card for details
F.01
Fault: Return temperature sensor - NTC plug not plugged in or has come loose, multiple plug on the PCB not plugged in correctly, interruption in cable harness, NTC sensor defective
F.10
Short circuit: Flow temperature sensor - NTC sensor defective, short circuit in the cable harness, cable/casing
F.11
Short circuit: Return temperature sensor - NTC sensor defective, short circuit in the cable harness, cable/casing
F.13
Short circuit: Domestic hot water cylinder temperature sensor - NTC sensor defective, short circuit in the cable harness, cable/casing
F.20
Safety switch-off: Overheating temperature reached - Incorrect earth connection between cable harness and product, flow or return NTC defective (loose connection), black discharge via ignition cable, ignition plug or ignition electrode
F.23
Safety switch-off: Temperature difference too great (NTC1/NTC2) - Pump blocked, insufficient pump output, air in product, flow and return NTC sensors connected the wrong way round
F.24
Safety switch-off: Temperature rise too fast - Pump blocked, insufficient pump output, air in product, system pressure too low, non-return valve blocked/incorrectly installed
F.25
Safety switch-off: Flue gas temperature too high - Break in plug connection for optional flue gas safety temperature limiter (STB), break in cable harness
F.27
Safety switch-off: Fault in flame detection - Moisture on the electronics, electronics (flame monitor) defective, gas solenoid valve leaking
Showing 11–20 of 33
F.28
Fault: Ignition unsuccessful when starting up - Gas meter defective or gas pressure monitor has triggered, air in gas, gas flow pressure too low, thermal isolator device (TAE) has triggered, incorrect gas restrictor, incorrect spare gas valve, fault on the gas valve, multiple plug on PCB incorrectly plugged in, break in cable harness, ignition system (ignition transformer, ignition cable, ignition plug, ignition electrode) defective, ionisation current interrupted (cable, electrode), incorrect earthing of product, electronics defective
F.29
Fault: Flame loss - Gas supply temporarily stopped, flue gas recirculation, incorrect earthing of product, ignition transformer has spark failure
F.32
Fan frost protection function active: Fan speed outside the tolerance values - Plug on fan not correctly plugged in, multiple plug on PCB not correctly plugged in, break in cable harness, fan blocked, Hall sensor defective, electronics defective
F.33
Fan frost protection function active: Air pressure switch fault - Pressure monitor has not switched or has switched at a fan speed value that is too high (insufficient air supply), Pressure monitor plug not correctly plugged in, pressure monitor defective, hose removed from between the pressure monitor and silencer, air/flue pipe blocked
F.49
eBUS fault: Voltage too low - Short circuit on eBUS, eBUS overload or two power supplies with different polarities on the eBUS
F.61
Fault: Gas valve control system - Short circuit/short to earth in cable harness for the gas valve, gas valve defective (coils shorted to earth), electronics defective
F.62
Fault: Gas valve switch-off control - Delayed switch-off of gas valve, delayed extinguishing of flame signal, gas valve leaking, electronics defective
F.63
Fault: EEPROM - Electronics defective
F.64
Fault: Electronics/sensor/analogue-to-digital converter - Flow or return NTC short circuited, electronics defective
F.65
Fault: Electronics temperature too high - Electronics overheating due to external influences, electronics defective
Showing 21–30 of 33
F.67
Value sent back by ASIC is incorrect (flame signal) - Implausible flame signal, electronics defective
F.68
Fault: Unstable flame (analogue input) - Air in gas, gas flow pressure too low, incorrect air ratio, incorrect gas restrictor, ionisation flow interruption (cable, electrode)
F.70
Invalid product code (DSN)
F.71
Fault: Flow/return temperature sensor
F.72
Fault: Deviation in the water pressure sensor/return temperature sensor
F.77
Fault: Condensate or smoke
F.78
Interruption to DHW outlet sensor at external controller
F.83
Fault: Burner temperature sensor
F.84
Fault: Flow/return temperature sensor
F.85
Fault: Temperature sensor
Showing 31–33 of 33
F.86
Fault: Underfloor heating contact
F.87
Fault: Electrodes
F.88
Fault: Gas valve