• Vaillant Fault Codes Explained

  • The most common Vaillant boiler fault codes.

    Though the fault code may point you to a certain part that may be faulty, it can sometimes mean that something else is at fault.

    These fault codes are only a guide as what to look for.

    Vaillant Boiler Fault Codes .

    If you have any Vaillant Boiler Fault Codes appear on the display and are not sure on how to resolve it.

    Contact us and arrange for an engineer to call and clear the faults and get your boiler up and running again.

    Common Vaillant Fault Codes 

    Fault Code F00

    Heating Flow NTC Thermistor Fault
     
        •    The Heating Flow NTC Thermistor Has Become Disconnected Or Has Gone Open Circuit (Should Read 12Kohms @ 20C)

     •    Wiring Harness Fault Or Connection Error Between The Heating Flow NTC Thermistor And The Main PCB
     
    Fault Code F10
    Heating Flow NTC Thermistor Fault
     
        •    There Is A Short Circuit On The Heating Flow NTC Thermistor     (Should Read 12Kohms @ 20C)
     
        •    Wiring Harness Fault Or Connection Error Between The Heating Flow NTC Thermistor And The Main PCB.
     
    Fault Code F11
    Heating Return NTC Thermistor Fault
     
        •    There Is A Short Circuit On The Heating Return NTC Thermistor (Should Read 12Kohms @ 20C)
     
        •    Wiring Harness Fault Or Connection Error Between The Heating Return NTC Thermistor And The Main PCB.
     
    Fault Code F12
    Domestic Hot Water Cylinder
     NTC Thermistor Fault
    (Not Applicable To This Appliance)
     
    Fault Code F13
    Internal Domestic Hot Water Storage Tank NTC Thermistor Fault
    (Not Applicable To This Appliance)
     
    Fault Code F17
    Solar Return Thermistor Fault
    (Not Applicable To This Appliance)
     
    Fault Code F20
    Overheat Fault
    The Flow Or Return Pipe In The Appliance Has Reached 97 Degrees C
     
    Fault Code F22
    Low System Water Pressure
        •    Water Leak Within The Boiler
     
        •    Water Leak Within The System
     
        •    The Pressure Relief Valve Has Activated Due To An Expansion Related Issue – Check Expansion Vessel & Heating System Water Volume
     
    Fault Code F23
    Maximum Temperature Differential Across The Heating Flow & Return Has Been Reached (35 Degrees C)
     
        •    Inadequate Pump Operation
        •    Blockage Or Air Lock Within The Appliance (No Water Movement)
        •    Blockage Or Air Lock In The Heating System (No Water Movement)
        •    Check Domestic Hot Water Heat Exchanger and Domestic Hot Water Heat Exchanger Filter For Debris If Fault Occurs On Hot Water Mode Only
        •    Check Resistance On The Heating Flow & Return NTC Thermistors To Ensure Accurate Temperature Monitoring (Should Read 12K ohms @ 20C)
     
    Fault Code F24
    Water Circulation Fault (Temperature Rise Greater Than 10 Degrees Celcius Per Second)
     
        •    Inadequate Pump Operation
        •    Isolation Valves Closed Under The Appliance
        •    Blockage Or Air Lock Within The Appliance (No Water Movement)
        •    Blockage Or Air Lock In The Heating System (No Water Movement)
        •    Check Domestic Hot Water Heat Exchanger and Domestic Hot Water Heat Exchanger Filter For Debris If Fault Occurs On Hot Water Mode Only
        •    Check Resistance On The Heating Flow & Return NTC Thermistors To Ensure Accurate Temperature Monitoring (Should Read 12K ohms @ 20C)
     
    Fault Code F25
     
                Flue Gas Temperature Too High (Not Applicable To UK Models)
     
    Fault Code F27
     
    Incorrect Flame Detection Fault (Flame Detection Even Though The Gas Valve Is Off)
     
        •    Damage On The Electrode Or The Ignition Lead
     
        •    Moisture Present On The Electronics
     
        •    Fault On The Spark Generator
     
        •    Fault On The Main PCB
     
    Fault Code F28
    Ignition Failure
     
        •    Insufficient Inlet Working Gas Pressure To The Appliance
        •    Flue Problem
        •    Bad Earth Connection
        •    Incorrect Gas Valve Adjustment
        •    Debris Within The Heat Engine (Burner Etc)
        •    Electrode Or Ignition Lead Fault
        •    Spark Generator Fault
        •    Faulty Gas Valve
     
    Fault Code F29
     
    Flame Failure During Operation
     
        •    Insufficient Inlet Working Gas Pressure To The Appliance
        •    Flue Problem
        •    Incorrect Gas Valve Adjustment
        •    Debris Within The Heat Engine (Burner Etc)
        •    Electrode Or Ignition Lead Issue
        •    Spark Generator Fault
        •    Faulty Gas Valve
     
    Fault Code F32
    Air Fault – (Fan Or Flue)
     
        •    Blockage In The Flue System
     
        •    Fan Rotation Speed Incorrect (Power To Fan But Fan Not Running)
     
        •    Loose Connection On The Wiring Harness Between The Fan And The Main PCB
     
    Fault Code F33
    Air Pressure Switch Fault – (Not Applicable To UK Models)
     
    Fault Code F49
     
    eBUS Voltage Error (Glow Worm Heating Controls Only)
     
        •    Overload On eBUS Connection On Main PCB
     
        •    Check External Glow Worm eBUS Heating Controls
     
        •    Check Wiring Between Glow Worm eBUS Controls And The Main PCB
     
        •    Check For Correct eBUS Output Voltage (22vdc) From Main PCB
     
    Fault Code F61
    Gas Valve Fault
     
        •    Loose Or Damaged Electrical Connection Between The Gas Valve & The Main PCB
     
        •    Faulty Gas Valve
     
        •    Main PCB Fault

    Fault Code F62
    Gas Valve Closure Fault
     
        •    Flame Presence Still Detected After A Demand Has Ceased Due To The Gas Valve Not Shutting Down Correctly                                        (Gas Valve Fault – Passing)
     
        •    Fault On Electronics (Power To The Gas Valve With No Demand)
     
    Fault Code F63
    Main PCB Memory Fault
     
        •    Loose Or Damaged Electrical Connection On The Main PCB
     
        •    The User Interface PCB Has Not Been Set Up Correctly By The Service Engineer (Incorrect Product Code Has Been Entered)
     
        •    Main PCB Fault
     
    Fault Code F64
     
    Rapid Fluctuation Of Heating Flow Or Return NTC Thermistors Due To Electrical Errors
     
        •    Loose Or Damaged Electrical Connections Between The Flow Or Return NTC Thermistors And The Main PCB
     
        •    Inconsistent Resistance On Heating Flow Or Heating Return NTC Thermistor Due To Thermistor Failure
     
        •    Main PCB Fault
     
    Fault Code F65
    Main PCB Temperature Too High
     
        •    Mains Input Voltage Problem
     
        •    Damaged Or Loose Electrical Connection On The Main PCB
     
        •    Main PCB Fault
     
    Fault Code F67
    Flame Signal Fault On The Main PCB
     
        •    Damaged Or Loose Electrical Connection On The Main PCB
     
        •    Main PCB Fault
     
        •    Mains Input Voltage Problem (Reverse Polarity, Poor Earth Etc)
     
    Fault Code F68
    Fluctuation Of Flame Signal
     
        •    Insufficient Inlet Working Gas Pressure To The Appliance
        •    Flue Problem
        •    Incorrect Gas Valve Adjustment (Poor Combustion)
        •    Debris Within The Heat Engine (Burner Etc)
        •    Electrode Or Ignition Lead Fault
        •    Spark Generator Fault
        •    Faulty Gas Valve
     
    Fault Code F70
    Incompatible Software
     
        •    Replacement User Interface PCB Has Not Been Set Up Correctly By The Service Engineer
     
        •    User Interface PCB Fault
     
        •    Main PCB Fault
     
    Fault Code F71
    Heating Flow NTC Thermistor Disconnected Or Defective (No Temperature Change When Burner Lit)
     
     
        •    Heating Flow NTC Thermistor Is Not Connected To The Flow Pipe On The Main Heat Exchanger Correctly
     
        •    Defective Heating Flow NTC Thermistor
     
    Fault Code F72
    Permanent Temperature Difference Between Heating Flow & Return NTC Thermistors (Thermistor Error)
     
        •    The Heating Flow NTC Thermistor Is Reading The Incorrect Resistance (Should Read 12Kohms @ 20C)
        •    Wiring Harness Fault Or Connection Error Between The Heating Flow NTC Thermistor And The Main PCB
        •    The Heating Return NTC Thermistor Is Reading The Incorrect Resistance (Should Read 12Kohms @ 20C)
        •    Wiring Harness Fault Or Connection Error Between The Heating Return NTC Thermistor And The Main PCB
        •    The Thermistors Have Been Reversed (Connected To The Wrong Pipes)
     
    Fault Code F73
     
    Low Water Pressure Sensor Fault
     
        •    Broken, Loose Or Damp Electrical Connection On The Wiring Harness Between The Low Water Pressure Sensor And The Main PCB
     
    Low Water Pressure Sensor Fault
    Fault Code F74
     
    Low Water Pressure Sensor Fault
     
        •    Broken, Loose Or Damp Electrical Connection On The Wiring Harness Between The Low Water Pressure Sensor And The Main PCB
     
        •    Low Water Pressure Sensor Fault
     
    Fault Code F75
     
    Low Water Pressure Sensor Fault Or Pump Proving Issue
     
        •    Low Water Pressure Sensor Faulty Or Blocked With System Debris
     
        •    Pump Not Running                                                                        
    (Water Pressure Sensor Needs To See A 50 mBar (0.05 Bar) Pressure Increase On Pump Start Within 10 Seconds)
     
        •    Flow Filter Blocked With Debris
     
        •    Expansion Vessel Air Charge Insufficient
     
    Fault Code F76
     
    Thermal Fuse Failure – Heat Exchanger Has Reached 160 Degrees C
    (Not Applicable To UK Models)

     
    Fault Code F77
     
    External Glow Worm Condensate Pump Fault
     
        •    Condensate Blockage
     
        •    Fault With Glow Worm Condensate Pump Or Associated Wiring
     
    Fault Code F78
    Compatibility Error Between The Boiler And The Glow Worm eBUS System Controls
     
        •    The Glow Worm eBUS System Controls Are Not Compatible With The Boiler
     
        •    Wiring Fault Between The Boiler And The Glow Worm eBUS System Controls
     
        •    Glow Worm eBUS System Controls Fault
     
        •    Loose Or Damaged Wiring Connection On The Main PCB
     
        •    Main PCB Fault
     
    Fault Code F83
     
    Insufficient Temperature Increase Once Burner Is Lit
     
        •    Low System Water Pressure
        •    Flow Or Return NTC Thermistors Out Of Calibration (Should Read 12Kohms @ 20C) Or Not Connected To Pipework Correctly
        •    Damaged Or Loose Connections On The Wiring Loom Between The NTC Thermistors And The Main PCB
        •    Low Heat Input Into The Heat Exchanger – Poor Thermal Performance Caused By Low Gas Rate, Incorrectly Adjusted Gas Valve, Or Restriction/Poor Heat Transfer Within The Combustion Chamber
     
    Fault Code F84
    Permanent Temperature Difference Between Heating Flow & Return NTC Thermistors (Thermistor Error)
     
        •    The Heating Flow NTC Thermistor Is Reading The Incorrect Resistance (Should Read 12Kohms @ 20C)
        •    Wiring Harness Fault Or Connection Error Between The Heating Flow NTC Thermistor And The Main PCB
        •    The Heating Return NTC Thermistor Is Reading The Incorrect Resistance (Should Read 12Kohms @ 20C)
        •    Wiring Harness Fault Or Connection Error Between The Heating Return NTC Thermistor And The Main PCB
        •    The Thermistors Have Been Reversed (Connected To The Wrong Pipes)
     
    Fault Code F85
    Flow Or Return NTC Thermistor Fault
     
        •    The Flow & Return NTC Thermistors Are Both Connected To The Same Pipe (Reading The Same Temperature)
     
        •    Faulty Flow Or Return NTC Thermistor

    Fault Code F86
    Overheat Thermostat From 3rd Party Underfloor Heating Control Has Activated (If Fitted)
     
        •    Check For Circulation Issues On Any Underfloor Heating Circuits
     
        •    If No 3RD Party Underfloor Overheat Thermostat Is Fitted To The Boiler, Check That The Link Wire Is Fitted Into The “B.off” Connection On Terminal X41 On The Main PCB
     
    Fault Code F87
    Electrode Fault
     
        •    Faulty Ignition Electrode Or Ignition Lead
     
    Fault Code F88
    Electrical Fault On The Gas Valve Circuit
     
        •    Loose Or Damaged Connection On The Wiring Harness Between The Main PCB and The Gas Valve
     
        •    Faulty Gas Valve (Short Circuit)
     
    Fault Code F89
     
    Electrical Fault On The Pump Circuit
     
        •    Loose Or Damaged Connection On The Wiring Harness Between The Pump and The Main PCB
     
        •    Faulty Pump (Short Circuit)

    These fault code as stated at the start are only a guide as to what the problem maybe.

    The boiler has a status code which can be checked by your gas safe installer.

    This code will explain how far the boiler has reached before the fault code appears. This is a good way of establishing where the fault maybe.

    Vaillant Faults Codes Explained. Vaillant Faults Codes Explained.