Vaillant Combi Boiler Error Codes


  1. Logical fault finding procedure
  2. Status codes
  3. Diagnostic codes
  4. Fault codes
  5. Fault memory
  6. Test programs

1-Logical Fault Finding Procedure:

These checks must be carried out before attempting to use the fault finding guide.

  1. Carry out electrical safety checks.
  2. Check that the external electricity supply to the boiler is on, and a supply of 230 V~ is present between boiler terminals ‘L’ and ‘N’.
  3. Check that the gas supply to the boiler is on, that it has been correctly purged and that an inlet pressure of 20 mbar is available at the gas valve. (See section ‘Gas Supply’).
  4. Ensure the heating system is full of water and charged to between 1 and 1.5 bar. If not, refill and vent the system. (See section ‘Filling the heating system’). Ensure boiler flow and return service valves are open.
  5. Check that the main on/off control is set to the ‘on’ position.
  6. Set the central heating temperature to maximum.
  7. Set the domestic hot water temperature to maximum (combination boilers only).
  8. Check that all external controls are on and calling for heat (if no external controls are fitted, boiler terminals 3 and 4 must be linked). Check that the boiler anti-cycling economiser is not engaged.

2-Status Codes:

The status codes that you can see on the display provides information about the current operating condition of the appliance. The display of the status codes can be called as follows:

Vaillant Combi Boiler Display of status codes
Vaillant Combi Boiler Display of status codes

Press the “i” key. The display shows the status code, e.g. S.04 for “Burner mode – Heating”.

The display of the status codes can be cancelled as follows:

  • Press the “i” key or
  • Do not press any key for about 4 minutes. The current heating flow temperature appears in the display again.
All models (heating mode)
S.00No heat demand
S.01Fan running
S.02Water pump running
S.03Ignition sequence
S.04Burner ignited
S.05Fan and pump running
S.06Fan over run
S.07Pump over run
S.08Anti cycling mode
ecoTEC combination boilers only (Domestic hot water mode)
S.10Hot water demand
S.11Fan running
S.13Ignition sequence
S.14Burner ignited
S.15Fan and pump running
S.16Fan over run
S.17Pump over run
ecoTEC combination boilers only (warm start)
S.20Warmstart demand
S.21Fan running
S.22Pump running
S.23Ignition sequence
S.24Burner ignited
S.25Fan and water pump running
S.26Fan over run
S.27Pump over run
S.28Anti cycling mode
All Boilers
S.30No heating demand from external controls
S.31Central heating thermostat knob turned off or no heat demand by the eBUS control unit
S.32Heat exchanger antifreeze active, as fan speed variation is too high. Appliance is within the waiting time of the operation block function
S.34Antifrost mode active
S.36No heating demand from low voltage controls
S.42Response from accessory modul or defective condensate pump is blocking burner operation
S.53Appliance is within the waiting period of the operation block function due to water shortage
S.54Appliance is within the waiting period of the operation block function due to water shortage
S.76Appliance is within the waiting period of the operation block function due to water shortage
S.96Return-sensor check is running, demand
S.97Waterpressure sensor check is running, demand
S.98Flow-/Return-sensor check is running, demand
Vaillant Combi Boiler Operator Control Panel
Vaillant Combi Boiler Operator Control Panel

3-Diagnostic Codes

In the diagnostic mode, you can change certain parameters or display more information. The diagnostic information is divided into two diagnostic levels. The second diagnostic level can be reached only after entering a password.


Access to the second diagnostic level must be used exclusively by a qualified technician.

First Diagnostic level

  • Press the “i” and “+” keys simultaneously. The display shows “d.00”.
  • Use the “+” or “–” keys to scroll through the desired diagnostic numbers of the first diagnostic level
  • Press the “i” key. The display shows the relevant diagnostic information.
  • If necessary, use the “+” or “–” keys to change the value
  • Save the new value by holding down the “i” key for approx. 5 seconds until the display no longer flashes.

You can end the diagnostic mode as follows:

  • Press the “i” and “+” keys simultaneously.
  • Do not press any key for approx. 4 minutes.

The current heating flow temperature appears in the display again.

Second diagnostic level

  • As described above in the first diagnostic level, scroll through the diagnostic number d.97.
  • Change the displayed value to 17 (password) and press the “i” button.

You are now in the second diagnostic level where all information from the first diagnostic level and the second diagnostic level is displayed. Scrolling and changing values and exiting the diagnostic mode is done as described in the first diagnostic level.

Note: After exiting the second diagnostic level, if you press “i” and “+” within 4 minutes, you will directly reach the second diagnostic level without having to enter the password again.

DisplayMeaningDisplay value/adjustable value
d.00Heating part loadAdjustable heating part load in kW
d.01Water pump over run time for heating mode1 - 60 min (factory setting: 5 min)
d.02Max. burner anti cycling period at 20 °C Flow temperature2 - 60 min (factory setting: 20 min)
d.03Hot water flow temperature reading (combination boiler only)in °C
d.04Current temperature for warm start sensor1 to 100 = on, 0 = off
d.05Flow temperature target value or return target value when return regulation is set.In °C, min. 30 °C and max. the value set in d.71 Limited by the eBUS controller
d.06Hot water temperature target valuein °C, 35 to 65 °C
d.07Warm start temperature target value. Storage temperature target valuein °C, 40 to 65 °C. in °C, 15 °C for left stop, then 40 to 70 °C
d.08External controls heat demand0 = no heat request (open) 1 = heat request (closed)
d.09Flow target temperature from external analogue regulator to terminal 7-8-9/eBUSin °C, minimum from ext. eBUS target value and target value terminal 7
d.10Status internal heating pump1, 2 = on, 0 = off
d.11Status external heating pump1 to 100 = on, 0 = off
d.13Hot water circulation pump1 to 100 = on, 0 = off
d.22Hot water demand1 = on, 0 = off
d.23Summer/Winter function1 = Winter, 0 = Summer
d.25Hot water activation via eBUS Control1 = yes, 0 = no
d.40Flow temperatureActual value in °C
d.41Return temperatureActual value in °C
d.47Outside temperatureActual value in °C
d.67Remaining burner anti cycling time in min
d.76 Appliance variant00 to 99
d.90Digital regulator status1 = identified, 0 = unidentified
d.91DCF status with connected external probe with DCF77 receiver0 = no reception, 1 = reception, 2 = synchronised, 3 = valid
d.97Activation of the second diagnostic levelPassword: 17
d.17Heating flow/return regulation changeover0 = flow, 1 = return
d.18 Pump mode0 = return, 1 = nonstop, 2 = winter
d.19Only in ecoTEC plus: Operating modes of the two-stage heating pump0 = Burner mode = 2, flow/return = 1 1 = Heating + flow =1, service water = 2 2 = Like 1, but speed in heating mode dependent on heating partial load (default setting) 3 = Always stage 2
d.27Switching accessory relay 1 in the accessory module1 = Circulation pump (default) 2 = Ext. pump 3 = Storage charging pump 4 = Flue gas flap/extractor hood 5 = External gas valve 6 = External error message
d.28Switching accessory relay 2 in the accessory module1 = Circulation pump 2 = Ext. pump (default) 3 = Storage charging pump 4 = Flue gas flap/extractor hood 5 = External gas valve 6 = External error message
d.30Control signal for both gas valves1 = on, 0 = off
d.33Fan speed target valuein rpm/10
d.34Fan speed actual valuein rpm/10
d.35Position of diverter valve0 = Heating; 1 = Hot water; 2 = Centre position
d.36Hot water flow sensor in l/min
d.44 Ionisation currentActual value [10nA]
d.50Offset for minimum speedin rpm/10, adjustment range: 0 to 250
d.51Offset for maximum speedin rpm/10, adjustment range: -99 to -0
d.60Number of safety temperature limiter cut offsQuantity
d.61Number of lock outsNumber of unsuccessful ignitions in the last attempt
d.64Average ignition timein seconds
d.65Maximum ignition timein seconds
d.68Unsuccessful ignitions in the first attemptQuantity
d.69Unsuccessful ignitions in the second attempt Quantity
d.70Set diverter valve position0 = Normal mode (factory setting) 1 = Centre position 2 = permanent heating position
d.71Maximum setting of heater control knobAdjustment range in °C: 40 to 85 (Factory setting: 75)
d.72Pump overrun time after charging an electronically controlled hot water storageAdjustment range in sec: 0, 10, 20 to 600 Factory setting for 800 series: 80 Factory setting for 600 series: 300
d.73Offset for warm start target valueAdjustment range: -15 K to +5 K
d.75Maximum charging time for a storage without own controllerAdjustment range in min: 20, 21, 22 to 90
d.77Storage partial loadAdjustment range in kW: appliance-specific Factory setting: max. output
d.78Storage charging temperature limitAdjustment range in °C 55 to 90
d.80Heating operating hours in h
d.81Water heating operating hoursin h
d.82Cycles in heating modeQuantity
d.83Cycles in hot water operation Quantity
d.84Maintenance indicator: Number of hours until the next maintenanceAdjustment range: 0 to 3000 h and “-” Factory setting: “-”
d.93DSN appliance variant settingAdjustment range: 0 to 99
d.96Factory setting1 = Resetting adjustable parameters to factory setting
Vaillant Combi Boiler Displayed Symbols
Vaillant Combi Boiler Displayed Symbols

4-Fault Codes

Fault codes take priority over all other display functions in the event of a system fault occurring. If multiple faults occur, the corresponding fault codes are displayed alternately for about two seconds each.

5-Fault Memory

The fault memory stores details of the ten most recent faults.

  • Press the ”i” and ”–” buttons simultaneously.
  • Use the ”+” button to scroll back through the list of memorised errors.

To cancel fault error memory display mode, proceed as follows:

  • Press the ”i” button below the display or
  • Do not touch any key for about four minutes. The display will now revert back to showing the current flow temperature.
F.00Flow–NTC open circuitNTC broken, NTC cable broken, Defective connection at NTC, Defective connection at electronics
F.01Return–NTC open circuitNTC broken, NTC cable broken, Defective connection at NTC, Defective connection at electronics
F.02Domestic hot water outlet NTC open circuitNTC-connector not plugged in or loose, NTC defective connector on the electronics not plugged in correctly, cable defective
F.10Flow NTC short circuitNTC defective,cable/casing shortcut
F.11Return NTC short circuitNTC defective, cable/casing shortcut
F.13Tank NTC short circuitNTC defective,short circuit in cable harness, cable/casing shortcut
F.20Safety temperature limiter by NTC activatedFlow-NTC not correctly thermal-connected or defective; appliance does not shut down
F.22Dry fireToo little water in the appliance, water pressure sensor defective, cable to pump or water sensor defective, pump blocked or defective, pump output too low
F.23Water shortage, temperature difference between flow and return NTC too largePump blocked or defective, pump output too low, flow and return NTC interchanged
F.24Water shortage, temperature rise too quickPump blocked, insufficient pump output, air in appliance, water pressure too low
F.27Incorrect sensing of flameFlame detector defective
F.28Appliance does not start: Attempts to ignite during start failedFaults in the gas supply such as: - Gas meter or gas pressure detector defective - Air in gas - Gas flow pressure too low - Fire protection tap has disengaged Faults in the gas valve, wrong gas setting, igniter (ignition transformer, ignition cable, ignition plug) defective, ionisation current stopped (cable, electrode), faulty earthing in appliance, electronics defective
F.29Flame goes off during operation and subsequent ignition attempts failedGas supply temporarily stopped, faulty earthing of appliance
F.32Fan speed variationFan blocked, plug not inserted correctly on fan, hall sensor defective, fault in cable harness, electronics defective
F.49eBUS undervoltageShort circuit on eBUS, overload on eBUS or two power sources on eBUS with different polarity
F.61Gas–valve control defectiveShort circuit/earth (ground) leak in cable harness to gas valves, gas valve assembly defective (earth/ground leak from coils), electronic control system defective
F.62Gas valve shutoff delayGas valve leaking, electronics defective
F.63EEPROM errorElectronics defective
F.64Electronics/NTC faultShort-circuit in flow or return NTC or electronics defective
F.65Electronics temperature too highElectronics too hot due to external effect, electronics defective
F.70No valid DSN in display and/or mainboardSpare part failure display and maiboard interchanged at same time and device specific number not adjusted
F.71Flow NTC reports constant value (stuck at)Flow NTC is defective
F.72Flow and/or return NTC faultFlow and/or return NTC is defective (tolerances too big)
F.73Water pressure sensor signal out of range (too low)Cable to water pressure sensor is broken or has a short-circuit at 0 V or water pressure sensor defective
F.74Water pressure sensor signal out of range (too high)Cable to water pressure sensor has a short-circuit at 5 V / 24 V or internal fault in water pressure sensor
F.75No pressure rise was detected on turning on the pumpWater pressure sensor or/and pump defective Too little water in appliance; check adjustable by-pass; connect external expension vessel to return
F.76Overheating protection on primary heat exchanger triggeredCable or cable connection of fuse in the primary heat exchanger defective, or primary heat exchanger defective
F.77condensate pump or feedback of accessorie blocks heatingcondensate pump defective or flume flap feedback triggered
F.78wrong configuration with accessorylink box VR65 connected to combination boiler
conno communication to mainboardconnection error display mainboard

6-Test Programs

Special functions can be triggered on the appliances by activating various test programs. These programs are given in detail in the table.

  • The test programs P.0 to P.6 will be started when “Power ON” is turned on and the “+” key is pressed for 5 s. The display shows “P.0”.
  • Press the “+” key to start counting the test number upwards.
  • Press the “i” to operate the appliance now and to start the test program.
  • Press “i” and “+” simultaneously to exit the test programs. You can also exit the test programs by not pressing any key for 15 minutes.
P.0Bleeding test program. The heating circuit and hot water circuit (combination boiler only) is bled via the automatic air vent (the cap on the automatic air vent must be loosened).
P.1Test program where the appliance is operated in full load after successful ignition
P.2Test program where the appliance is operated with minimum gas volume (ignition gas volume) after successful ignition
P.3not available
P.4not available
P.5Test program for the safety temperature limit check; appliance heats up by by-passing a regulating shutdown through the flow regulator until the shutoff temperature of 97 °C is achieved.
P.6Filling test program. The diverter valve moves to the centre position

Vaillant Combi Boiler Manual PDF

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