Vaillant Combi Boiler Error Codes List and How to Fix

Vaillant combi boiler error codes are crucial for users. These codes provide essential information to understand the device’s performance and troubleshoot issues effectively. Identifying the correct code in case of a malfunction is key to initiating an efficient repair process.

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.

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:

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

Operator Control Panel

Vaillant Combi Boiler Operator Control Panel
Vaillant Combi Boiler Operator Control Panel

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 level.

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.

d.00Heating part load
d.01Water pump over run time for heating mode
d.02Max. burner anti cycling period at 20 °C Flow temperature
d.03Hot water flow temperature reading (combination boiler only)
d.04Current temperature for warm start sensor
d.05Flow temperature target value or return target value when return regulation is set.
d.06Hot water temperature target value
d.07Warm start temperature target value. Storage temperature target value
d.08External controls heat demand
d.09Flow target temperature from external analogue regulator to terminal 7-8-9/eBUS
d.10Status internal heating pump
d.11Status external heating pump
d.13Hot water circulation pump
d.22Hot water demand
d.23Summer/Winter function
d.25Hot water activation via eBUS Control
d.40Flow temperature
d.41Return temperature
d.47Outside temperature
d.67Remaining burner anti cycling time
d.76 Appliance variant
d.90Digital regulator status
d.91DCF status with connected external probe with DCF77 receiver
d.97Activation of the second diagnostic level
d.17Heating flow/return regulation changeover
d.18 Pump mode
d.19Only in ecoTEC plus: Operating modes of the two-stage heating pump
d.27Switching accessory relay 1 in the accessory module
d.28Switching accessory relay 2 in the accessory module
d.30Control signal for both gas valves
d.33Fan speed target value
d.34Fan speed actual value
d.35Position of diverter valve
d.36Hot water flow sensor
d.44 Ionisation current
d.50Offset for minimum speed
d.51Offset for maximum speed
d.60Number of safety temperature limiter cut offs
d.61Number of lock outs
d.64Average ignition time
d.65Maximum ignition time
d.68Unsuccessful ignitions in the first attempt
d.69Unsuccessful ignitions in the second attempt
d.70Set diverter valve position
d.71Maximum setting of heater control knob
d.72Pump overrun time after charging an electronically controlled hot water storage
d.73Offset for warm start target value
d.75Maximum charging time for a storage without own controller
d.77Storage partial load
d.78Storage charging temperature limit
d.80Heating operating hours
d.81Water heating operating hours
d.82Cycles in heating mode
d.83Cycles in hot water operation
d.84Maintenance indicator: Number of hours until the next maintenance
d.93DSN appliance variant setting
d.96Factory setting

Displayed Symbols

Vaillant Combi Boiler Displayed Symbols
Vaillant Combi Boiler Displayed Symbols

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.

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.00NTC broken, NTC cable broken, Defective connection at NTC, Defective connection at electronics
F.01NTC broken, NTC cable broken, Defective connection at NTC, Defective connection at electronics
F.02NTC-connector not plugged in or loose, NTC defective connector on the electronics not plugged in correctly, cable defective
F.10NTC defective,cable/casing shortcut
F.11NTC defective, cable/casing shortcut
F.13NTC defective,short circuit in cable harness, cable/casing shortcut
F.20Flow-NTC not correctly thermal-connected or defective; appliance does not shut down
F.22Too 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.23Pump blocked or defective, pump output too low, flow and return NTC interchanged
F.24Pump blocked, insufficient pump output, air in appliance, water pressure too low
F.27Flame detector defective
F.28Faults 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.29Gas supply temporarily stopped, faulty earthing of appliance
F.32Fan blocked, plug not inserted correctly on fan, hall sensor defective, fault in cable harness, electronics defective
F.49Short circuit on eBUS, overload on eBUS or two power sources on eBUS with different polarity
F.61Short 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 leaking, electronics defective
F.63Electronics defective
F.64Short-circuit in flow or return NTC or electronics defective
F.65Electronics too hot due to external effect, electronics defective
F.70Spare part failure display and maiboard interchanged at same time and device specific number not adjusted
F.71Flow NTC is defective
F.72Flow and/or return NTC is defective (tolerances too big)
F.73Cable to water pressure sensor is broken or has a short-circuit at 0 V or water pressure sensor defective
F.74Cable to water pressure sensor has a short-circuit at 5 V / 24 V or internal fault in water pressure sensor
F.75Water pressure sensor or/and pump defective Too little water in appliance; check adjustable by-pass; connect external expension vessel to return
F.76Cable or cable connection of fuse in the primary heat exchanger defective, or primary heat exchanger defective
F.77condensate pump defective or flume flap feedback triggered
F.78link box VR65 connected to combination boiler
conconnection error display mainboard

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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