BoilerFaultCodes D.118-1
CO sensor fault: Heater short circuit
Vaillant ecoTEC exclusive 627 Fault codes & diagnostics
120 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.
System Gas 2016-present
GC Numbers 41-694-0241-694-02
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Versions & GC numbers
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Severity at a glance
Each cell = one fault code. Hover to identify. 120 Unrated
Which version do you have?
The GC number on your boiler's data badge identifies the exact appliance and production years, as recorded in the UK Product Characteristics Database.
| GC number | Appliance (register name) | Produced |
|---|---|---|
| 41-694-02 | ecoTEC exclusive 627 VU 256/5-7 (H-GB) | 2016–present |
| 41-694-02 | ecoTEC exclusive 627 VU 256/5-7 (H-GB) | 2016–present |
Appliance names and production years are taken from the UK Product Characteristics Database (the SAP/SEDBUK register). Where a GC number is also printed in this model's own manufacturer manual, both sources were checked to agree.
Just want the most common Vaillant ecoTEC exclusive 627 faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes
All 120 documented codes
Tap any card for details
D.118-2
CO sensor fault: Heater open circuit
D.118-3
CO sensor fault: Heater temperature control fault
D.118-4
CO sensor fault: Heater temperature plausibility check not OK
D.118-5
CO sensor fault: Sensor short circuit/open circuit
D.118-6
CO sensor fault: Reference resistance measurement not OK
D.118-7
CO sensor fault: Sensor impedence too high
D.118-8
CO sensor fault: Standby reference resistance not OK
D.118-9
CO sensor fault: EEPROM error
D.118-10
CO sensor fault: Sensor open circuit
Showing 11–20 of 120
D.118-11
CO sensor fault: Not used
D.118-12
CO sensor fault: Sensor plausibility test fault
D.118-13
CO sensor fault: Electrical power consumption too low
D.118-14
CO sensor fault: Electrical power consumption too high
D.118-15
CO sensor fault: Reference voltage too low
D.118-16
CO sensor fault: Reference voltage too high
F.00
Interruption:Flowsensor | NTCplugnotpluggedinorhascomeloose,multipleplugonthePCBnotpluggedincorrectly,interruptionincableharness,NTCdefective
F.01
Interruption:Returnsensor | NTCplugnotpluggedinorhascomeloose,multipleplugonthePCBnotpluggedincorrectly,interruptionincableharness,NTCdefective
F.02
Interruption:DHWoutletsensor | OnlyinconjunctionwithF.91 NTCdefective,NTCcabledefective,defectiveplugconnectiononNTC,defectiveplugconnectionontheactoSTORelectronics
F.03
Interruption:Cylindersensor | OnlyinconjunctionwithF.91 NTCdefective,NTCcabledefective,defectiveplugconnectiononNTC,defectiveplugconnectionontheactoSTORelectronics
Showing 21–30 of 120
F.10
Shortcircuit:Flowsensor | NTCdefective,shortcircuitincableharness,cable/housing
F.11
Shortcircuit:Returnsensor | NTCdefective,shortcircuitincableharness,cable/housing
F.12
Shortcircuit:DHWoutletsensor | OnlyinconjunctionwithF.91 NTCdefective,shortcircuitincableharness,cable/housing
F.13
Shortcircuit:Cylindersensor | Combinationproduct:Warmstartsensor/cylindersensorshortcircuit CombinationproductwithactoSTOR:Shortcircuitcylindersensor(NTC)onlyincombinationwithF.91 NTCdefective,shortcircuitincableharness,cable/housing
F.20
Safetyswitch-off:Temperaturelimiter | Incorrectearthconnectionbetweencableharnessandproduct,floworreturnNTCdefective(looseconnection),straysparkviaignitioncable,ignitionplugorignitionelectrode. Onlyinliquefiedpetroleumgasoperationorincascademode:Thedifferentialpressuresensorwasnotreplacedwithabypassvalve;thebypassvalveisnotfunctional
F.22
low water pressure (product switches off)
F.23
Safetyswitch-off:Temp.spreadtoolarge | Pumpblocked,insufficientpumpoutput,airinproduct,flowandreturnNTCconnectedthewrongwayround
F.24
Safetyswitch-off:Temp.incr.toofast | Pumpblocked,insufficientpumpoutput,airinproduct,systempressuretoolow,non-returnvalveblocked/incorrectlyinstalled
F.25
Safetyswitch-off:Fluetemp.toohigh | Breakinplugconnectionforoptionalfluegassafetycut-out(SCO),breakincableharness
F.26
Fault:Fuelvalvenotworking | Gasvalveassemblysteppermotornotconnected,multipleplugonthePCBnotpluggedincorrectly,interruptionincableharness,gasvalveassemblysteppermotordefective,electronicsdefective
Showing 31–40 of 120
F.27
Safetyswitch-off:Flamesimulation | Moistureontheelectronics,electronics(flamemonitor)defective,gas solenoidvalveleaking
F.28
Start-upfailure:Ignit.unsuccessful | Gasmeterdefectiveorgasflowmonitorhastriggered,airingas,gas flowpressuretoolow,thermalcut-outhastriggered,condensaterouteblocked,incorrectgasinjector,incorrectsparepartgasvalveassembly,valueinD.052doesnotcorrespondtotheprintedvalueonthecurrent gasvalveassembly,faultonthegasvalveassembly,multipleplugon PCBincorrectlypluggedin,breakincableharness,ignitionsystem(ignitiontransformer,ignitioncable,ignitionplug,ignitionelectrode) defective,ionisationflowinterrupted(cable,electrode),incorrectearthing ofproduct,electronicsdefective
F.29
Operatingfailure:Ignit.unsuccessful | Gassupplytemporarilystopped,fluegasrecirculation,condensateroute blocked,defectiveearthingofproduct,ignitiontransformerhasspark failure
F.32
Fault:Fan | Plugonfannotcorrectlypluggedin,multipleplugonPCBnotcorrectlypluggedin,breakincableharness,fanblocked,Hallsensordefective,electronicsdefective
F.33
Pressureswitch | Check:Cableharness,vacuumhose(blockage),supplyair/fluegas route(blockage),panel(correcttype),fluepipe(length),airpressure sensor,settings(ifnecessary,switchD.132tomultiple-flueconfigura- tion),pressureswitch,fan.
F.35
Fault: Air/fluegas duct
F.42
Fault: Coding resistor
F.49
Fault: eBUS
F.55
Fault related to all-gas sensor
F.56
Safety switch-off: CO limit exceeded
Showing 41–50 of 120
F.57
Fault: Measuring program
F.61
Fault: Fuel valve actuation
F.62
Fault: Fuel valve switch-off delay
F.63
Fault: EEPROM
F.64
Fault: Electronics/sensor
F.65
Fault: Electronics temp.
F.67
Fault: Electronics/flame
F.68
Fault: Flame signal unstable
F.70
Fault: Invalid Device Specific Number
F.71
Fault: Flow sensor
Showing 51–60 of 120
F.72
Fault: Flow/return sensor
F.73
Fault: Water press. sensor
F.74
Fault: Water press. sensor
F.75
Fault: Pump/water shortage
F.77
Fault: Flue non-ret. valve/condens. pump
F.78
Interrupt.: DHW outlet sensor on ext. contr.
F.80
Fault: actoSTOR inlet sensor
F.81
Fault: cylinder charging pump
F.82
Fault: Ext. current anode
F.83
Fault: NTC temp. gradient
Showing 61–70 of 120
F.84
Fault: NTC temp. diff. implausible
F.85
Fault: NTCs fitted incorrectly
F.90
Fault: Communication
F.94
Fault: Vortex and differential pressure
S.00
Heating: No heat demand
S.01
Heating mode: Fan start-up
S.02
Heating mode: Pump pre-run
S.03
Heating mode: Ignition
S.04
Heat requirement status
S.05
Heating mode: Pump/fan overrun
Showing 71–80 of 120
S.06
Heating mode: Fan overrun
S.07
Heating mode: Pump overrun
S.08
Heating mode: Anti-cycling time
S.09
Heating mode: Measuring program
S.10
DHW demand
S.11
DHW mode: Fan start-up
S.13
DHW mode: Ignition
S.14
Heat requirement status
S.15
DHW mode: Pump/fan overrun
S.16
DHW mode: Fan overrun
Showing 81–90 of 120
S.17
DHW mode: Pump overrun
S.19
DHW mode: Measuring program
S.20
DHW demand
S.21
DHW mode: Fan start-up
S.22
DHW mode: Pump pre-run
S.23
DHW mode: Ignition
S.24
DHW mode: Burner on
S.25
DHW mode: Pump/fan overrun
S.26
DHW mode: Fan overrun
S.27
DHW mode: Pump overrun
Showing 91–100 of 120
S.28
DHW anti-cycling time
S.29
DHW mode: Measuring program
S.30
No heat demand: Controller
S.31
No heat demand: Summer mode
S.32
Waiting time deviation: Fan speed
S.33
Waiting time: Air monitor
S.34
Heating mode: Frost protection
S.36
Target value for ext. controller lower than 20°C
S.37
Waiting time: Deviation in fan speed
S.39
Contact thermostat triggered
Showing 101–110 of 120
S.40
Product is in Comfort protection mode
S.41
Water pressure too high
S.42
Fluenon-returnflapclosed | Fluenon-returnflapresponseblocksburneroperation(onlyinconjunctionwithaccessoryVR40)orcondensatepumpdefective;heatrequirementisblocked
S.46
Comfortprotection:Minimumload,lossofflame | Comfortprotectionmode,flamelossatminimumload
S.53
Waitingtime:Watershortage | Productiswithinthewaitingperiodofthemodulationblock/operatingblockfunctionasaresultofwaterdeficiency(flow/returnspreadtoolarge)
S.54
Waitingtime:Watershortage | Productiswithinthewaitingperiodoftheoperatingblockingfunctionasaresultofwaterdeficiency(temperaturegradient)
S.55
Waitingtime:COsensor | Waitingperiod:COsensor
S.56
Waitingtime:COlimitvalueexceedance | Waitingperiod:COlimitvalueexceedance
S.57
Waitingtime:Measuringprogram | Calibrationunsuccessful.Waitingperiod,comfortprotectionmode
S.58
Burnermodulationlimitation | Modulationlimitationduetonoise/wind
Showing 111–120 of 120
S.59
Waitingtime:Watercirculationvol. | Minimumcirculationwatervolume
S.76
Servicemessage:Checkwaterpressure | Systempressuretoolow.Topupwater.
S.86
Product remains in comfort safety mode
S.88
Purgingprogrammeisrunning | Purgingprogrammeisrunning
S.92
Watercirculationvolumeself-test | Watercirculationvolumeself-test
S.93
Fluegasmeasurementnotpossible | Fluegasanalysisnotpossiblebecausenotallmeasuringprogrammeshaveyetrun
S.96
Returntemperaturesensorself-test | Returnsensortestrunning,heatingdemandsareblocked.
S.97
Waterpressuresensorself-test | Waterpressuresensortestrunning,heatingdemandsareblocked.
S.98
Flow/returntemperaturesensorself-test | Flow/returnsensortestrunning,heatingdemandsareblocked.
S.99
Vaillantself-test | Self-test
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